UC-NRLF 


SB    7D 


EXCHANGE 


A  Study  of  the  Factors  Influencing 


THE 


Improvement  of  the  Potato 


PRESENTED  TO  THE 


FACULTY  OF  THE  UNIVERSITY  OF  ILLINOIS 

URBANA,  ILLINOIS,  U.  S.  A. 


AS  A 


Thesis  for  the  Degree  of  Doctor  of  Philosophy 


JUNE,  1907 


BY 


EDWARD  MURRAY  EAST,  M.  S. 


PUBLISHED 

BY  THE  UNIVERSITY  OF  ILLINOIS 

AGRICULTURAL  EXPERIMENT  STATION 

AS  BULLETIN  No.  127 


UNIVERSITY  OF  ILLINOIS 


Agricultural  Experiment  Station 


BULLETIN  NO.  127 


A  STUDY  OF  THE  FACTOES  INFLUENCING 
THE  IMPEOVEMENT  OF  THE  POTATO 


BY  EDWARD  M.  EAST 


URBANA,  ILLINOIS,  AUGUST,  1908 


TABLE  OF  CONTENTS 

PAGES. 

Introduction 375 

1.  The  Use  of  Other  Species 378 

2.  The  Original  Plant   380 

Original  Habitat 380 

Introduction  to  Cultivation 380 

Two  Varieties  Introduced    382 

3.  The  Modern  Plant 385 

Structure  and  Characteristics   385 

Varieties  of  To-day 387 

Modern  Potato  Breeders   390 

4.  Methods  of  Breeding 391 

General  Basis   391 

Precautions  in  Comparative  Tests 394 

Correlations    395 

5.  The  Inheritance  of  Characters  in  Tuber  Selections 398 

Theory    398 

Experimental  Evidence   403 

6.  Hypothesis  of  Degeneration   410 

Analysis  of  the  Question 410 

Biological  Evidence   413 

Experimental  Evidence   . .  .  . 414 

7.  Discontinuous  Variations 417 

8.  Graft  Hybrids    418 

9.  Quality 419 

Historical   .. , ; 419 

Sxperimeblajlx*:  •«;,.- 422 

A  I •  .**  Qomposition . 0£ ..Different  Parts 422 

'  '  *  *'  :  "Sahlplmg**.. /.•;,.•.«! 423 

Relations   Between  Total   Nitrogen  Content   and 

Quality    423 

Relations  Between  Dry  Matter  and  Quality 425 

Physical  Structure  and  Quality 426 

Other  Factors  Influencing  Quality 429 

10.  Variations  in  Chemical  Composition  as  a  Basis  for  Im- 

provement   437 

Selections  for  Planting  in  1902 439 

Selections  for  Planting  in  1903 443 

11.  General  Statements 447 

Bibliography    450 


A  STUDY  OF  THE  FACTORS  INFLUENCING  THE 
IMPROVEMENT  OF  THE  POTATO* 

BY  EDWARD  M.  EAST. 

INTRODUCTION 

Either  because  it  possesses  no  strong  flavor  to  dull  the  appetite, 
or  possibly  on  account  of  its  antiscorbutic  properties,  the  common 
potato  Solatium  tuber osum  L,.,  has  overcome  seemingly  insurmount- 
able obstacles  in  its  claim  upon  the  public  taste  and  has  become  a 
close  rival  to  our  cereal  staff  of  life.  The  high  cost  of  production 
and  general  uncertainty  of  the  return,  combined  with  the  cost  of 
transportation  of  a  perishable,  bulky  product,  would  seem  to  be  ad- 
verse factors  which  might  preclude  any  general  increase  in  grow- 
ing the  crop.  Such  has  not  been  the  case,  however,  and  the 
potato,  like  other  crops,  has  increased  greatly  in  a6reage  in  lo- 
calities best  suited  to  it,  notably  the  sandy  soils  of  the  northern 
states.  These  soils  seem  to  be  so  pre-eminently  fitted  for  its  growth 
that  the  crops  are  highly  profitable  even  after  deducting  the  cost  of 
shipping  long  distances.  During  the  last  ten  years,*  *  the  six  states 
of  Maine,  New  York,  Pennsylvania,  Michigan,  Wisconsin  and  Iowa 
have  furnished  an  average  of  one-half  of  the  total  crop  of  the 
United  States.  In  other  sections  of  the  country  where  the  growing 
of  large  crops  is  more  unlikely  from  natural  reasons,  as  inhospitable 
soil  or  climate,  the  cost  of  production  has  been  high,  and  over- 
production at  times  (as  in  1895-6)  has  had  a  very  disastrous  effect 
upon  the  price,  occasioning  great  loss  to  the  producer.  This  state 
of  affairs  is  in  a  great  measure  due  to  the  fact  that  in  these  sec- 
tions the  acreage  per  grower  is  small,  and  the  business  is  not  suf- 
ficiently organized  to  make  possible  long  distance  shipping,  which 
would  partially  overcome  the  great  local  fluctuation  in  price. 

The  annual  consumption  of  potatoes  per  -capita  in  the  United 
States  for  a  period  of  thirty  years  is  given  by  the  Twelfth  Census 
as  three  and  one-half  bushels,  and  when  the  amount  available  for 
human  consumption  is  smaller  than  this, — as  has  beevn  the  case  in 
the  last  few  years, — the  price  precludes  their  use  for  other  purposes. 

*Submitted  to  the  Faculty  of  the  Graduate  School  of  the  University  of  Illinois  in  partial 
fulfillment  of  the  requirements  for  the  degree  of  Doctor  of  Philosophy,  March,  1907. 

**U.  S.  Dept.  of  Agri.  Yearbook,  1905. 

375 

239369 


376  BULLETIN  No.  127.  \August, 

This  has  left  capital  invested  in  starch  mills  completely  unpro- 
ductive, as  the  limiting  price  within  which  the  manufacturer  can 
compete  is  forty  cents  per  barrel  of  two  and  one-half  bushels.  There 
is  no  doubt  but  that  the  repeal  of  the  tax  upon  alcohol  for  indus- 
trial purposes  will  furnish  a  channel  for  the  utilization  of  all  future 
excess  of  production  over  that  used  for  human  consumption,  should 
the  manufacturers  of  starch,  glucose,  dextrin  and  desiccated  prod- 
uct,— who  can  pay  a  slightly  higher  price, — be  unable  to  utilize  it. 
At  the  present  rate  of  increase  of  our  population,  however,  the  an- 
nual increase  of  production  for  human  food  alone  must  be  from 
3,000,000  to  5,000,000  bushels ;  and  an  increase,  which  would  be  a 
factor  in  the  production  of  alcohol  at  all  comparable  with  that  of 
Germany,  would  have  to  be  many  times  that  amount. 

The  broad  problems  which  confront  the  grower  who  has  to  face 
these  demands,  are,  increased  yields  per  acre  and  the  development 
of  varieties  adapted  to  specific  purposes.  In  the  first  instance  suit- 
able soil,  available  plant  food,  and  proper  methods  of  tillage  and  of 
combating  disease  will  do  much ;  but  here  as  well  as  in  the  second 
case,  probably  the  possibility  for  as  great  an  advance  lies  in  the 
province  of  the  plant  breeder. 

The  matter  of  variety  efficiency  to  produce  tubers  in  large  quan- 
tities may  be  regarded  as  a  desired  accompaniment  to  all  strains,  no 
matter  what  other  particular  characters  they  may  possess.  The  spe- 
cial characters,  with  the  possession  of  which  new  varieties  should  be 
originated,  are  (i)  an  increase  in  nutritive  value,  (2)  an  improve- 
ment in  table  quality,  and  (3)  a  higher  starch  content.  Coupled 
with  the  possession  of  each  of  these  qualities  should  be  the  very 
important  character  of  resistance  to  disease. 

Since  the  potato  is  one  of  the  world's  cheapest  food  sources,  if 
there  is  a  possibility  of  finally  obtaining  varieties,  which,  without 
being  perfect  foods,  yet  would  furnish  a  more  nearly  proper  ratio 
of  protein  and  carbohydrates;  it  would  be  an  inestimable  boon  to 
the  world's  poor,  for  protein  is  a  much  more  expensive  food  con- 
stituent than  starch.  This  problem  is  inseparably  linked  with  im- 
provement in  general  table  quality,  for  quality  must  in  some  man- 
ner be  correlated  with  composition.  On  the  other  hand,  varieties 
should  be  originated  which  yield  a  large  amount  of  starch  per  acre, 
for  the  use  of  those  growing  for  the  starch,  glucose  or  alcohol 
manufacturer.  It  is  recognized  that  at  the  present  price  of  produc- 
tion, maize  is  a  much  cheaper  source  of  alcohol  than  potatoes ;  but 
with  the  American  taste  for  high  starch  potatoes,  such  potatoes 
would  be  used  as  food  except  in  times  of  over  production,  until 


IMPROVEMENT  OF  THE  POTATO.  377 

cheaper  methods  of  production  and  better  varieties  make  the  potato 
a  competitor  with  the  cereals  for  manufacturing  purposes. 

This  study  deals  with  such  questions  as  have  naturally  arisen  in 
trying  to  form  a  basis  for  practical  work  in  potato  improvement; 
and  includes  an  examination  of  the  literature  bearing  upon  the  pos- 
sibilities of  attaining  this  end.  The  principles  underlying  practical 
work  in  potato  improvement  are  very  broad, — much  too  broad  to 
be  adequately  discussed  in  a  single  paper, — and  yet  it  seems  impos- 
sible to  separate  them  into  narrow  lines  without  ignoring  principles 
which  are  essential  to  the  work.  For  this  reason  it  has  been  thought 
best  to  consider  briefly  such  of  these  as  are  indispensable,  without 
regard  as  to  whether  in  every  case  they  have  been  touched  in  the 
experimental  work.  No  attempt  has  been  made  to  discuss  historical, 
agricultural  or  economic  data,  however,  except  in  so  far  as  such 
subjects  relate  to  the  improvement  of  the  potato  in  desirable  hered- 
itary qualities.  A  considerable  amount  of  literature  has  made  its 
appearance  since  the  beginning  of  the  experimental  work  in  1901 ; 
but  we  have  endeavored  to  give  a  resume  of  the  present  status  of 
knowledge  of  the  subjects. 

The  writer  desires  to  express  his  obligation  to  the  Directors  of 
the  Illinois  and  Connecticut  Agricultural  Experiment  Stations, 
E.  Davenport  and  E.  H.  Jenkins,  through  whom  was  made  possible 
the  use  of  laboratory  and  other  facilities  of  these  stations ;  and  who 
have  given  much  helpful  advice.  Especial  acknowledgment  is  made 
to  Dr.  C.  G.  Hopkins  under  whose  direction  the  study  was  under- 
taken, and  who  has  been  a  constant  source  of  advice  and  encour- 
agement. 


378  BULLETIN  No.  127.  [August, 

i.  THE  USE  OF  OTHER  SPECIES 

The  plant  which  bears  the  tuber  which  we  call  the  potato,  and 
which  name  has  been  extended  to  the  whole  plant,  has  a  recorded 
history  of  only  three  hundred  years,  it  having  been  introduced  into 
Europe  about  the  end  of  the  sixteenth  century.  Its  botanical  char- 
acter caused  it  to  be  called  Solatium  tuberosum  by  Gaspard  Bauhin 
(86)  in  his  Phytopinax,  printed  at  Bale  in  1596.  This  name  was 
followed  by  Linnaeus  when  binomial  nomenclature  was  introduced. 

There  are  several  other  members  of  the  genus  which  bear  tubers, 
but  none  has  yet  become  of  commercial  importance.  About  twenty 
tuber-bearing  kinds  of  Solanum  have  been  at  different  times  classed 
as  separate  species.  J.  G.  Baker  (6)  has  given  us  probably  our  best 
classification,  after  having  made  a  thorough  examination  of  all 
species  at  Kew,  the  British  Museum,  and  the  Lindley  Herbarium, 
as  well  as  many  growing  specimens.  He  concludes  that  there  are 
only  six  distinct  species :  S.  tuberosum  Linn.,  S.  Maglia  Schlecht, 
S.  Commersonii  Dun.,  S.  cardiopJiyllum  Lind.,  S.  Jamesii  Torr.  and 
S.  oxycarpum  Schiede.  Later,  (7)  he  places  S.  Maglia  as  a  va- 
riety of  S.  tuberosum  which  reduces  the  number  of  species  to  five. 

Solanum  Commersonii  Dun.  has  been  shown,  by  Labergerie 
(65)  to  be  in  all  probability  the  most  promising  of  the  other  species, 
in  its  commercial  possibilities.  In  his  extended  investigations,  it 
showed  a  great  tendency  to  produce  bud  variations  in  color  which 
were  permanent,  and  which  when  propagated  showed  great  differ- 
ences in  the  production  of  tubers,  immunity  to  disease,  etc.  A  vio- 
let variation  showed  absolute  immunity  to  late  blight  Phytophthora 
infestans  (Mont.)  De  By.,  for  three  years,  while  plants  of  S.  tu- 
berosum growing  near  were  stricken..  The  yield  was  as  high  as 
100,000  K.  per  hectare  with  a  composition  much  the  same  as  the 
common  potato.  Rev.  J.  R.  Lawrence  of  North  Middleboro,  Mas- 
sachusetts, has  recently  stated,  however,  that  his  plants  have  not 
been  immune  to  late  blight. 

S.  Maglia  Schlecht.  of  Chili,  S.  immite  Dun.  of  Peru,  and  S.  ver- 
rucosum  Schlect.  of  Mexico,  have  all  been  mentioned  as  species  and 
varieties  especially  worthy  of  being  tried  in  the  hopes  of  finding 
strains  which  by  selection  might  become  of  commercial  value  and 
be  immune  to  certain  diseases,  or  with  which  the  same  end  might  be 
reached  by  hybridization  with  5*.  tuberosum.  No  valuable  com- 
mercial strains  from  these  sources,  however,  have  yet  been  pro- 
duced. 

Stuart  (92)  found  in  1904  that  S.  Commersonii  and  5.  poly- 


iQoS.]  IMPROVEMENT  OF  THE  POTATO.  379 

adenium  were  quite  resistant  to  late  blight,  while  S.  stoloniferum 
was  not.  In  his  later  (93)  report  of  1905,  they  all  showed  a  high 
percentage  of  infection.  None  of  these  species  or  varieties  gave 
marketable  tubers  in  his  tests,  but  they  had  hardly  been  cultivated 
by  him  long  enough  to  have  become  adapted  to  Vermont  conditions. 
De  Candolle  (22  p.  49)  mentions  that  S.  verrucosum  is  not  dis- 
ease resistant. 

It  seems  unlikely  from  past  results,  that  there  will  be  any  great 
progress  made  through  straight  selections  of  other  species,  if  we 
except  S.  Commersonii.  This  species  has  been  thus  far  very  unsat- 
isfactory in  the  United  States,  but  there  is  in  it  still  cause  for  ex- 
periment. It  is  very  variable  in  its  habits  of  growth,  length  of 
stolons,  shape  of  tubers  and  other  important  characters ;  hence  there 
may  in  time  be  some  promising  strains  isolated.  Until  we  have 
such  strains  established,  there  wkl  probably  be  little  good  from 
hybridizing  mediocre  elementary  species  with  the  common  potato, 
for  the  hybridization  is  effected  with  difficulty. 

For  two  seasons  the  writer  has  had  under  observation  some 
plants  grown  from  tubers  of  Labergerie's  stock  imported  by  J.  J.  H. 
Gregory  and  son,  Marblehead,  Massachusetts.  Phytophthora  in- 
festans  has  not  been  troublesome  during  either  of  these  seasons; 
hence,  no  data  have  been  obtained  regarding  the  comparative  re- 
sistance of  the  plants  to  the  fungus.  I  am  compelled  to  state,  how- 
ever, that  in  no  character  off  leaf,  stem,  flower  or  tuber,  is 
the  plant  different  from  common  purple  tubered  varieties  of  S.  tu- 
berosum. Either  there  has  been  some  mistake  in  Labergerie's 
seemingly  careful  work,  and  there  has  been  a  mixture  with  tubers 
of  S.  tuberosum;  or  we  must  conclude  that  there  have  been  bud 
mutations  in  at  least  five  or  six  characters  of  S.  Cornmersonii,  giving 
a  plant  indistinguishable  from  S.  tuberosum.  The  truth  of  the  latter 
conclusion  would  give  us  a  unique  phenomenon  that  is  of  extreme 
importance  to  science,  and  the  case  must  be  confirmed  before  it  is 
accepted  as  a  fact. 

Our  plants  have  flowered  freely,  but  viable  pollen  has  been  pro- 
duced in  extremely  small  quantities.  Numerous  attempts  at  hybrid- 
izing with  S.  tuberosum  have  all  failed. 


380  BULLETIN  No.  127.  [August, 

2.  THE  ORIGINAL  PLANT 

ORIGINAL  HABITAT 

A.  De  Candolle  (22  p.  46)  states  that  Solanutn  tuber osum  was 
unknown  to  the  aborigines  of  eastern  South  America,  although 
$.  Commersonii  was  common  as  a  wild  plant.  Along  the  western 
coast,  however,  the  potato  was  well  known  and  its  cultivation  dif- 
fused from  Chili  to  New  Grenada. 

Pedro  Ciec.a  de  Leon  (86  p.  5)  in  his  "Spanish  Chronicles  of 
Peru,"  makes  the  first  written  mention  of  the  potato  in  1550. 

"In  the  neighborhood  of  Quito,"  he  says,  "the  inhabitants  have  besides  maize, 
two  other  plants  which  serve  as  a  great  portion  of  their  food,  papas  and  quiniia. 
The  papas  has  roots  enlarged  into  tubercles,  which  are  covered  with  a  more  or 
less  hard  skin;  these  when  cooked  have  a  pulp  nearly  as  tender  as  a  puree  of 
chestnuts.  When  dried  in  the  sun  to  preserve  them,  they  are  called  chumo,  and 
are  thus  preserved  for  future  use.  The  fruit  produces  a  stalk  similar  to  the 
poppy.  The  quiniia  is  a  plant  about  the  height  of  a  man  and  has  leaves  like 
the  blite  of  Mauritania,  and  a  small  seed  either  red  or  white  in  color,  from 
which  is  prepared  a  drink,  and  a  food  comparable  to  our  rice." 

Lopez  de  Gomara  (86  p.  5)  in  his  "Histoire  generale  des  Indes" 
(1154)  and  Augustin  de  Zarate  in  his  "Histoire  de  la  Decouverte 
et  de  la  Conquete  du  Perou"  (1555)  also  speak  of  this  "papas" 
which  is  still  the  Indian  name  of  the  potato.  Jerome  Cardan  in  his 
curious  work  entitled  "De  Rerum  Varietate"  (Bale  1557)  expresses 
himself  in  these  terms  on  the  same  subject : 

"On  the  height  of  the  mountains  in  the  country  of  Peru,  the  papas  are  like 
a  species  of  truffle  which  is  served  in  place  of  bread,  and  are  also  dried  in  the 
sun.  It  is  thus  nature  has  wisely 'provided  for  all  needs.  When  they  are  dried 
they  are  called  ciuno.  Certain  people  have  found  means  to  enrich  themselves 
by  transporting  this  commodity  into  Potosi.  It  is  said  that  the  root  has  a  stem 
similar  to  that  of  Argemone.  The  papas  have  the  form  of  chestnuts  but  have 
a  more  agreeable  taste.  They  are  eaten  cooked  or  better  as  I  said  made  into 
flour.  They  are  found  as  commonly  among  other  tribes  of  this  peninsular  as 
they  are  among  the  inhabitants  of  the  province  of  Quito." 

Other  writers  through  the  latter  half  of  the  sixteenth  century, 
and  travelers  and  writers  later,  (22)  show  conclusively  that  the  po- 
tato was  and  still  is  wild  in  Chili,  but  that  the  probability  is  that  the 
plants  found  seemingly  wild  in  Peru,  were  either  escaped  from  cul- 
tivation or  were  allied  species  for  which  it  had  been  mistaken. 

INTRODUCTION  TO  CULTIVATION 
i 

The  Spanish  conquerers  of  Peru  introduced  the  potato  into 
Spain  and  Portugal  sometime  between  1535,  the  date  of  the  con- 


1908.] 


IMPROVEMENT  OF  THE  POTATO. 


381 


FIG.   i.     THE  FIRST  POTATO  INTRODUCED  INTO  EUROPE.     FROM   CLUSIUS'  WATER- 
COLOR  OF  1588.     (AFTER  E.  ROZE.) 


382  BULLETIN  No.  127.  [August, 

quest,  and  1585,  whence  the  cultivation  spread  into  Italy  sometime 
early  in  the  seventeenth  century.  From  here,  the  potato  in  all  prob- 
ability went  to  Austria,  from  Austria  to  Germany,  Germany  to 
Switzerland,  and  from  Switzerland  to  France. 

Spanish  voyagers  also  probably  introduced  the  tubers  to  the 
English  settlers  in  Virginia;  at  any  rate  they  were  being  culti- 
vated there  before  1585,  and  were  sent  to  England  at  the  time  of 
Sir  Walter  Raleigh's  voyages  to  Virginia  though  not  by  Raleigh 
himself.  From  England,  potato  cultivation  spread  very  rapidly  to 
Ireland  which  needed  a  cheap  food  crop,  and  by  the  beginning  of 
the  eighteenth  century,  it  had  become  one  of  its  staples.  Their  uni- 
versal use  on  the  island  from  this  time  forward  brought  them  their 
common  name  of  the  Irish  potato.  This  nickname  is  not  to  be  won- 
dered at  for  Ireland  still  leads  in  the  use  of  potatoes  with  an  annual 
per  capita  consumption  of  twenty-five  bushels,  or  seven  times  that 
of  the  United  States.* 

Two  VARIETIES  INTRODUCED 

We  have  seen  that  Bauhin  wrote  the  first  description  of  the 
potato  in  1596,  but  as  he  in  all  probability  received  his  specimen 
from  Clusius,  to  the  latter  should  be  given  the  credit  of  the  descrip- 
tion of  the  first  cultivated  potatoes.  The  specimens  described  by 
Clusius  were  sent  to  him  in  1588  by  Philippe  Sivry,  Seigneur  of 
Waldheim  and  Governor  of  Mons,  who  had  received  them  from 
Italy  at  the  hands  of  the  Papal  Legate.  The  accompanying  plate 
of  Clusius  is  from  Roze's  colored  plate  made  from  the  original  and 
has  not  been  available  before  in  an  English  publication.  Speaking 
of  his  reproduction  Roze  says  : 

"This  colored ^late  is  a  faithful  reproduction  from  the  most  ancient  docu- 
ment we  possess  on  the  introduction  of  the  potato  into  Europe.  For  the  orig- 
inal water-color  which  dates  1589  is  kept  with  other  writings  and  books  of  this 
epoch  (of  which  the  authenticity  is  certain)  in  the  archives  of  the  ancient  six- 
teenth century  printings  and  preserved  in  its  original  state  at  Anvers,  Belgium, 
at  the  Musee  Plantin-Moretus.  The  writing  on  the  Latin  manuscript  which 
has  also  been  reproduced  from  the  original  water-color  is  thus  'taratoufli  a 
Philippe  de  Sivry  acceptum  Viennae  26  Januarii  1588.  Papas  Peruanum  Petri 
CieQae,'  and  is  a  fac-simile  of  the  writing  of  the  celebrated  botanist  Charles  de 
L'Ecluse  of  Arras,  more  commonly  known  to  the  world  under  his  Latin  name 
Clusius. 

"This  proves  to  be,  not  the  date  of  the  reception  of  the  water-color,  repre- 
senting a  flower  stalk  with  two  potatoes  which  had  only  been  sent  to  Charles 
L'Ecluse  in  1589  by  Philip  de  Sivry,  Seigneur  de  Walhain  et  Gouverneur  de  la 
Ville  Mons  en  Hainaut,  but  that  of  two  tubers  and  one  fruit  berry  of  the 

*Mayo-Smith:   Statistics  and  economics,  p.  38. 


i<po8.]  IMPROVEMENT  OF  THE  POTATO.  383 

potato  that  Carrolus  Clusius  Atrebatis,  in  his  Rariorum  Plantarum  Historia 
published  by  Moretus  in  1601,  declared  to  have  been  sent  to  him  by  Philippe  de 
Sivry  a  Vienne  at  the  beginning  of  the  year  1888.  These  two  tubers  and  the 
seeds  from  this  fruit  have  produced  all  the  potatoes  which  at  the  end  of  the 
sixteenth  century  were  cultivated  in  Austria,  Germany,  Switzerland  and  France." 

Judging  from  this  plate  and  from  what  Clusius  says  in  his  "Rar- 
iarum  plantarum  historia"  (17),  the  plant  has  changed  little  under 
cultivation  except  probably  to  give  fewer  and  larger  tubers.  The 
larger  tuber  shown  in  the  figure  is  one  and  three-fourths  inches  long 
and  would  weigh  about  35  grams.  He  states  in  his  work  that  the 
plant  then  yielded  as  many  as  fifty  tubers  of  unequal  size  and  from 
one  to  two  inches  long.  This  would  still  be  considered  a  good  yield 
for  a  two-year  seedling  and  is  commonly  not  exceeded  here  the 
first  or  second  year  by  unacclimated  varieties  imported  from  Europe. 

The  other  European  introduction, — that  into  Great  Britain, — 
was  first  described  by  John  Gerard  in  his  "Herbal,"  published  in 
London  in  1597.  This  has  usually  been  given  as  the  first  descrip- 
tion of  the  potato  and  the  accompanying  figure  is  a  reproduction  of 
his  wood-cut  as  given  in  the  edition  of  1636.  Gerard,  however, 
knew  of  Clusius'  description  as  is  shown  in  the  following  quotation. 
He  says,  speaking  of  the  potato : 

"It  groweth  naturally  in  America,  where  it  was  first  discovered  as  reporteth 
Clusius,  since  which  time  I  have  received  roots  hereof  from  Virginia  otherwise 
called  Norembega,  which  grow  and  prosper  in  my  garden  as  in  their  own 
native  country." 

It  is  remarkable  that  these  two  introductions  into  Europe  were 
made  with  two  different  varieties  of  S.  tuber osum.  The  one  de- 
scribed by  Clusius  which  probably  produced  the  earlier  varieties  of 
northern  Europe,  had  reddish  tubers  and  light  purple  blossoms.  The 
later  introduction  into  England  described  by  Gerard  possessed  light 
brown  to  yellowish  tubers  and  violet  to  almost  white  flowers. 

The  variations  in  the  descendents  of  these  two  varieties  have 
been  almost  entirely  restricted  to  the  tubers.  The  ash-leaved  varie- 
ties of  England  constitute  an  exception,  where  the  variation  is  in  the 
shape  of  the  leaf.  This  fact  is  important  from  two  points  of  view. 
First,  it  indicates  that  there  has  been  but  little  correlated  variation 
between  underground  and  aerial  parts,  and  hence  we  are  unlikely  to 
find  plant  characters  by  which  we  can  with  reasonable  certainty  re- 
ject unsuitable  types.  Second,  zuith  so  little  visible  variation  in  the 
plant,  there  is  likely  to  be  narrow  variability  in  resistance  to  fungus 
diseases,  should  such  resistance  be  due  to  structural  differences. 


384 


BULLETIN  No.  127. 


[August, 


FIG.  2.    THE  FIRST  POTATO  INTRODUCED  INTO  ENGLAND.     (FROM  WOODCUT  IN  GER- 
ARD'S HERBAL.    ED.  OF  1636.) 


1908.] 


IMPROVEMENT  OF  THE  POTATO. 


385 


3.  THE  MODERN  PLANT 
STRUCTURE  AND  CHARACTERISTICS 

The  potato  is  an  annual,  and  in  its  original  state  reproduced 
freely  by  seeds.  The  tubers  were  then  so  small  that  it  is  doubtful 
whether  the  plant  would  have  been  preserved  to  us  by  this  alternate 
means  of  reproduction.  At  present,  however,  many  varieties  never 
or  at  most  rarely  seed,  and  the  plant  has  become  virtually  a  peren- 
nial through  its  tubers. 

Baker  (6)  gives  the  following  technical  description  of  a  wild 
plant : 

"Leaves  pseudo-stipulate,  a  fully  developed  one  about  half  a  foot  long, 
with  seven  to  nine  finely  pilose,  oblong-acute,  large  leaflets,  the  side  ones  stalked 
and  unequally  cordate  at  the  base,  the  one  to  two  lowest  pairs  much  dwarfed, 
leaving  a  naked  petiole  about  an  inch  long;  the  rhacis  furnished  with  numerous 
small  leaflets  interspaced  between  those  of  full  size.  The  flowers  arranged  in 
compound  terminal  cymes,  with  long  peduncles;  pedicels  hairy,  articulated 
about  the  middle.  Calyx  hairy,  one-fourth  to  one-third  inch  long,  teeth  deltoid- 
cuspidate,  as  long  as,  or  a  little  longer  than,  the  campanulate  tube.  Corolla  dark 
lilac,  subrotate,  nearly  an  inch  in  diameter,  pilose  externally;  segments  deltoid, 
half  as  long  as  the  tube.  Anthers  bright  orange-yellow,  linear-oblong,  nearly 
one-fourth  inch  long,  filaments  very  short.  Berry  perfectly  globose,  smooth,  un- 
der an  inch  in  diameter." 

This  description  perfectly  fits  the  cultivated  potato  of  today,  as 
Baker  has  already  noted,  with  the  exception  that  the  lobes  of  the 
calyx  are  now  a  little  more  pointed. 


I 


FIG.  3.    PARTS  OF  POTATO  FLOWER. 

a.  Back  side  of  anther.  c.  Front  side  of  anther. 

b.  Pistil.  d.  Cross  section  of  anther. 

e.  Tops  of  anther  showing  the  openings. 


386  BULLETIN  No.  127.  [August, 

The  flowers  in  the  cultivated  plants  vary  in  color  from  white 
to  purple,  and  usually  two  clusters  growing  side  by  side  make  up 
the  compound  cyme.  They  possess  an  entire,  five  pointed  corolla 
with  five  stamens  with  large  fleshy  anthers  enclosing  the  pistil. 
Darwin  quotes  Makenzie  (68)  as  describing  a  variety  which  pro- 
duced two  sorts  of  flowers,  the  one  double  and  sterile  and  the  other 
single  and  fertile.  The  sexes  mature  at  the  same  time;  the  anth- 
ers open  at  the  top  like  a  small  cup,  and  in  certain  cases  split  for  a 
short  distance.  The  pollen  is  usually  wind  carried,  as  the  flowers 
produce  no  nectar  and  are  not  greatly  frequented  by  insects.  Muller 
(75  p.  425)  and  Fruwirth  (43  v.  3  p.  6)  each  mention  several  spe- 
cies, however,  that  they  had  noted  around  the  flowers.  Darwin 
considered  self-fertilization  possible;  and  from  the  comparative 
ease  with  which  I  have  obtained  "selfed"  fruits  in  twenty-six  dif- 
ferent varieties,  and  from  the  rarity  of  insect  visitors,  I  believe  self- 
fertilization  to  be  natural  to  the  species.  The  flowers  open  between 
five  and  six  o'clock  a.  m.  in  this  climate  and  slightly  close  about 
dusk.  The  pollen  is  usually  shed  on  the  second  day  of  blooming 
and  it  is  then  that  the  pistil  is  most  receptive.  With  profuse  seed- 
ing varieties  the  flowers  wither  about  the  fourth  day. 

Fraser  (37  p.  5)  states  that  out  of  three  hundred  varieties  many 
of  which  he  has  grown  for  several  years,  he  has  found  none  which 
do  not  bloom  at  some  time  of  their  life.  In  opposition  to  this  view, 
Rev.  J.  R.  Lawrence,  of  North  Middleboro,  Massachusetts,  who 
grows  some  eight  hundred  varieties  asserts  that  some  varieties 
never  bloom.  However  this  may  be  it  is  certainly  true  that  there 
is  a  great  variation  in  varieties  in  the  power  to  bloom  and  still  more 
in  their  ability  to  set  seed.  Some  varieties  evidently  go  for  years 
without  blooming,  others  bloom  whenever  there  are  optimum  condi- 
tions of  climate' and  season.  I  have  found  varieties  setting  seed 
freely  in  Waupaca  county,  Wisconsin,  when  during  the  same  season 
plants  from  the  same  fields  of  the  year  before  produced  no  seed 
in  Champaign  county,  Illinois.  There  are  varieties  which  develop 
clusters  of  buds  which  fall  without  opening,  and  many  more  which 
produce  flowers,  all  of  which  fall  without  setting  fruit.  Some  of 
the  anthers  in  the  latter  varieties  contain  no  pollen,  others  shriveled 
pollen  grains  containing  no  protoplasm,  while  still  others  produce 
viable  pollen  though  never  (in  my  experience)  in  large  quantities. 
The  blossoms  separate  at  certain  fixed  places  on  the  stem  where  a 
ring  is  formed  by  layers  of  tissue  drying.  Liebscher  (66)  states 
that  fragrance  is  correlated  with  yield  of  pollen  but  I  have  found 
no  noticeable  fragrance  in  American  varieties. 


ipod?.]  IMPROVEMENT  OF  THE  POTATO.  387 

It  is  a  common  idea  that  the  potato  does  not  set  fruit  as  freely 
now  as  formerly,  and  the  explanation  has  been  given  that  the  pro- 
duction of  large  quantities  of  tubers  has  led  to  the  degeneration  of 
the  seeding  power.  It  is  true  that  many  of  our  finest  varieties 
bloom  seldom  and  rarely  set  seed,  yet  this  does  not  seem  to  be  a  cor- 
relation with  yielding  power,  for  some  of  our  best  varieties  bloom 
freely,  and  under  proper  conditions,  set  seed. 

Fraser  (37)  has  shown  this  variation  in  blooming  to  have  been 
natural  nearly  two  hundred  years  ago.  He  says : 

"Mark  Catesby,  who  was  in  this  country  in  1722-1726,  wrote  that  'in  Vir- 
ginia and  to  the  north  thereof,  they  (potatoes)  are  annuals,  and  produce  no 
flowers,  while  in  Carolina  and  the  Bahama  Islands,  they  produce  flowers.  Many 
varieties  existed  at  that  time  particularly  in  Virginia,  and  five  kinds  were  com- 
mon: the  Common,  Bermudas,  Brimstone,  Carrot  and  Claret  potatoes.  The 
Bermuda  potato  was  the  only  one  that  had  a  white  flower,  the  flowers  of  all 
the  other  kinds  being  purple.  This  was  the  only  variety  that  had  a  white  skin 
and  was  white  fleshed.  It  was  round  in  shape,  more  tender,  and  more  delicate 
to  raise  than  the  others,  and  did  not  keep  so  well." 

In  Connecticut,  many  excellent  varieties  do  not  seed  and  cannot 
be  used  as  stock  to  breed  from,  but  varieties  representing  all  of  our 
favored  commercial  variations  in  shape  and  color,  can  be  obtained 
which  produce  seed.  In  other  climates,  notably  Maine,  Minnesota 
and  Wisconsin  many  of  the  non-seeding  varieties  of  Connecticut 
produce  pollen  and  seed  comparatively  freely.  This  makes  it  pos- 
sible to  obtain  hybrid  seed  from  varieties  where  the  female  parent 
at  least  is  acclimated  and  adapted  to  these  soils,  for  the  female  or- 
gans appear  to  be  always  perfectly  normal. 

The  tuber  of  the  potato  is  a  swollen,  underground  stem,  with 
its  eyes  equivalent  to  the  leaf  buds  of  an  aerial  stem,  and  which  are 
arranged  more  or  less  spirally  in  each  case.  The  main  underground 
stem  of  the  plant  varies  in  length  with  the  depth  of  planting.  At 
intervals  on  this  underground  stem,  stolons  are  sent  out,  at  the  ex- 
tremities of  which  are  found  the  tubers.  Varieties  differ  greatly  in 
the  length  of  these  stems  and  the  manner  in  which  the  tubers  are 
formed.  A  variety  to  be  of  commercial  value  should  have  very 
short  stolons  and  bear  only  one  tuber  at  the  end.  There  should  be 
no  branches  from  the  bud  end  of  the  tuber,  as  is  sometimes  the  case. 

The  physiology  of  tuber  formations  is  discussed  at  length  by 
Vochting  (101). 

VARIETIES  OF  TODAY 

At  present,  there  are  in  the  United  States  over  one  thousand 
named  varieties.  This  large  list  contains  many  names  that  repre- 


388 


BULLETIN  No.  127. 


[August, 


sent  potato  plants  and  tubers  having  the  same  characteristics,  and 
which  are  indistinguishable,  even  to  an  expert  potato  buyer.  In 
some  cases  this  has  been  due  to  the  actual  stealing  of  meritorious 
varieties  by  unscrupulous  dealers,  who  have  put  out  the  stock  under 
a  different  name,  and  given  it  a  foothold  by  persistent  advertising. 
More  often,  however,  the  duplication  has  been  done  by  potato  fan- 
ciers who  are  growing  seedlings  from  naturally  pollenized  seed,  and 
who  obtain  similar  strains  which  are  saleable  to  seedsmen,  as  new 
varieties  for  the  single  reason  that  they  have  been  obtained  from 
seed.  If  the  yield  is  fair,  and  the  tuber  is  of  a  popular  type,  the 
restless  fancy  of  the  American  public  for  something  new,  gives  a 
ready,  though  temporary  market  for  the  stock  from  the  new  seed- 
ling no  matter  if  it  is  slightly  inferior  to  its  already  established 
prototype.  I  have  seen  at  least  twenty  named  varieties  of  the  Car- 
man No.  3  type  (short-oval-flat  with  white  skin)  which  were  ab- 
solutely indistinguishable  in  shape,  color,  and  manner  of  growth, 
and  if  the  popularity  of  this  type  continues  there  will  undoubtedly 
be  an  annual  addition  to  this  list  of  names. 

Of  real  variations  in  varieties,  productive  efficiency  or  ability  to 
excel  in  crop  production  under  like  conditions  of  environment,  is 
the  character  of  greatest  importance  at  present  to  the  grower.  The 
astonishing  adaptability  of  some  varieties  as  compared  to  others, 
to  certain  soils  and  climates  is  shown  in  the  following  table  from 
varieties  grown  at  the  Connecticut  Agricultural  Experiment  Station 
in  1906,  on  plots  of  poor  but  uniform  soil  with  like  treatment  as 
to  planting,  cultivation,  fertilizers,  etc.  To  what  these  differences 
are  due:  whether  there  are  many  different  elementary  species  in 
$.  tuberosum  whose  characters  have  been  recombined  into  innumer- 
able varieties  by  hybridization;  or  whether  they  are  due  merely  to 
desirable  fluctuations  that  regress  slowly  because  of  bud  propaga- 
tion is  unknown. ,  The  fact  of  the  differences  remains. 

TABLE  i.    VARIATION   OF  VARIETIES   IN   PRODUCTIVENESS  UNDER  UNIFORM   FIELD 

CONDITIONS 


Variety. 

Yield  per  acr 

e  in  bushels. 

Marketable 

Seconds. 

K.  Six  Weeks  

18  7 

89 

E.  Ohio  

36  2 

U7 

E.  Norther  

57  2 

on   -3 

Minister  

74  7 

73  f\ 

~Ei.  Manistee  

79  3 

14   0 

Twentieth  Century  

102.7 

11  7 

State  of  Maine  

113  2 

17  ^ 

Green  Mountain  

137.7 

18  7 

IMPROVEMENT  OF  THE  POTATO.  389 

Owing  to  the  great  local  differences  in  soil  fertility  and  physical 
character,  this  character  of  productiveness  must  be  determined  by 
trial  in  every  climate  and  for  every  soil.  It  is  pre-eminently  the 
desired  character  of  the  grower,  as  all  other  characters  are  at 
present,  more  or  less  fancy  demands  of  the  consumer,  and  concern 
the  grower  only  so  far  as  the  urgency  of  the  demand  affects  the 
price.  Some  of  the  characters  that  generally  receive  attention  from 
modern  growers  as  conducive  to,  or  correlative  with,  yield, — are 
disease  resistance,  character  of  haulm  and  leaf,  time  of  maturity, 
and  length  of  stolons. 

The  first  character  is  well  discussed  in  a  recent  publication  of 
Jones  (59).  In  the  writer's  experience  there  is  certainly  a  varia- 
tion in  the  ability  of  different  varieties  to  resist  attacks  of  early  and 
late  blight,  but  whether  the  differences  noticed  within  the  variety  are 
due  to  anything  but  a  different  time  of  infection  is  questionable. 
That  there  are  wide  individual  variations  in  respect  to  susceptibility 
toward  the  physiological  trouble,  tip  burn,  is  more  apparent. 

The  haulm  should  be  vigorous,  covering  the  ground  when  in 
full  growth,  but  upright  and  bushy  rather  than  long  and  sprawling. 
The  meeting  of  the  plants  in  the  row  conserves  the  soil  moisture 
when  cultivation  can  no  longer  be  given  while  an  upright,  bushy 
haulm  favors  ease  in  the  farm  operations,  and  probably  tends  to 
lessen  disease  infection. 

In  general,  varieties  yield  in  proportion  to  their  growing  sea- 
son, provided  there  is  entire  maturity  before  frost.  Varieties  which 
are  still  green  at  the  close  of  the  season  have  large  numbers  of  tu- 
bers set  but  a  great  many  of  these  fail  to  reach  a  marketable  size 
and  the  plant  is  killed  while  'still  containing  much  dry  matter  which 
should  have  been  transferred  to  the  tubers.  Length  of  stolon  seems 
to  be  a  very  strong  variety  characteristic  and  permanent  when  ob- 
tained. The  length  should  never  exceed  three  or  four  inches,  al- 
though with  5.  Commersonii,  it  sometimes  reaches  the  extreme 
length  of  ten  feet. 

Variety  characteristics  which  are  prominent  and  which  depend 
almost  entirely  on  the  public  taste  to  be  of  value,  are  those  of  tuber 
shape  and  skin  character.  There  are  varieties  possessing  every  pos- 
sible shape,  but  they  may  be  roughly  divided  into  the  oval  and  the 
round  and,  if  we  wish  to  make  a  third  class,  the  kidney  shaped. 
The  popular  shapes  at  present  are  quite  flat,  the  short-oval-flat  be- 
ing the  most  desired.  There  may  be  a  sufficient  reason  for  this,  as 
Fischer  (32  v.  2  p.  49)  found  that  flat-round  tubers  or  flat-oval 
tubers  showed  a  correlation  with  starch  content.  The  actual  reason 
for  popularity  would  seem  to  be  the  fact  that  potatoes  of  this  shape 
give  a  greater  weight  per  measure,  in  which  manner  they  are  usu- 
ally retailed.  The  eyes  of  potatoes  of  this  type  are  also  compara- 
tively shallow,  thereby  giving  less  waste. 


390  BULLETIN  No.  127.  [August, 

Skin  color  seems  to  be  purely  a  matter  of  preference  without  a 
real  reason,  there  having  been  no  correlations  shown  between  par- 
ticular colors  and  other  desirable  qualities.  White  to  light  brown 
are  the  colors  most  sought  in  the  northern  markets  while  red 
skinned  varieties  find  ready  sale  in  the  south.  Krzymowski  (63) 
states  that  rough  skinned  varieties  are  highest  in  starch  content; 
and  it  is  generally  believed  that  this  is  also  correlated  with  re- 
sistance to  scab. 

MODERN  POTATO  BREEDERS 

Growing  potato  seedlings  has  been  a  fascinating  work  for 
thousands  of  gardeners  throughout  the  United  States,  who  have 
taken  up  the  work  merely  as  a  recreation  and  have  planted  seeds  of 
unknown  parentage,  rejecting  year  by  year  those  which  gave  poor 
yields  or  had  characteristics  which  were  thought  undesirable  for 
market.  The  mere  fact  of  numbers  has  brought  from  this  desultory 
work  a  large  number  of  commercial  varieties,  a  conspicuous  ex- 
ample being  the  Burbank  potato.  This  variety  was  the  progeny 
of  a  natural  seed  ball  found  in  a  garden  by  Mr.  Luther  Burbank 
when  he  was  a  boy.  As  we  only  hear  in  such  cases  from  those 
who  are  successful,  there  is  no  way  of  judging  the  percentage  of 
failures;  but  judging  from  those  who  have  come  to  my  personal 
knowledge,  and  from  talking  with  seed  merchants,  certainly  not 
over  one  or  two  percent  of  these  growers  ever  produce  a  commer- 
cial variety.  Varieties  which  come  into  prominence  today  show 
increasing  evidence  of  the  work  of  the  breeder  who  studies  his 
ground  carefully  and  works  toward  a  definite  end.  It  is  probably 
not  too  much  to  say  that  90  percent  of  our  present  potato  crop  is 
from  varieties  originated  by  scientific  breeders,  such  as  the  late 
E.  S.  Carman.  The  small  amount  of  published  matter  concerning 
the  present  day  workers  in  potato  breeding  and  their  methods 
makes  correspondence  necessary  for  organized  work,  and  a  list  of 
some  of  the  prominent  workers  is  given  here. 

United  States:  O.  H.  Alexander,  Charlotte,  Vt. ;  Marvin  Bovee,  North- 
ville,  Mich.;  E.  L.  Coy,  West  Hebron,  N.  Y. ;  W.  E.  Johnson,  Bowdoinham, 
Me.;  J.  R.  Lawrence,  E.  Raynham,  Mass.;  Chas.  Norcross,  Litchfield,  Me.;  C.  S. 
Pringle,  Charlotte,  Vt. ;  Hiriam  Presley,  Port  Huron,  Mich. ;  E.  <L.  Roser, 
Cleveland,  O. 

Great  Britain:  James  Clark,  Christ  Church,  Hants;  Robert  Fenn,  Holm- 
wood,  Sulhampstead,  Reading;  C.  Fidler,  Reading;  A.  Findlay,  Markinch;  T.  A. 
Scarlett,  Edinburgh;  A.  W.  Sutton  &  Son,  Reading. 

France:  Tibulle  Collot,  Maizieres;  Forgeot  &  Cie.,  Paris;  Leonard  Lille, 
Lyon;  Hyacinthe  Rigault,  Groslay;  Joseph  Rigault,  Groslay;  Vilmorin-An- 
drieux  et  Cie.,  Paris. 

Germany:  Cimbal,  Fromdorf  bei  Miinsterberg;  Flieszbach,  Curow,  Pom- 
mern;  A.  Kirsche,  Pfiffelbach;  von  Lochow,  Petkus;  G.  Rlodel,  Tagewerben 
bei  Weiszenfels. 


1908.]  IMPROVEMENT  OF  THE  POTATO.  391 

4.  METHODS  OF  BREEDING 
GENERAL  BASIS 

In  potato  breeding,  there  are  four  steps  before  the  worker: 
i.  Selection  of  varieties  for  improvement.  2.  Discovery  of  valuable 
bud-variations.  3.  Selections  of  mother  plants,  and  their  crossing. 
4.  Comparison  and  selection  of  the  progeny.  It  is  the  province  of 
the  breeder  to  discover  the  best  methods  for  prosecuting  this  work, 
— the  obstacles  in  the  way,  and  the  probabilities  of  success  under 
different  conditions.  The  means  of  propagation  of  the  potato  is  in 
most  of  these  steps  a  disadvantage.  The  comparatively  simple 
methods  of  the  seed  propagated  annuals  and  biennials  are  seri- 
ously complicated,  and  the  advantage  of  grafting  held  forth  by  the 
orchard  fruits  is  lacking. 

In  taking  the  first  step,  it  is  in  some  cases  impossible  to  select 
varieties  with  characters  that  are  desirable,  to  combine  with  those 
possessing  other  characters,  because  of  the  large  number  of  varieties 
which  produce  no  viable  pollen.  A  great  number  of  varieties  must 
be  grown,  and  the  matter  as  to  whether  fertile  pollen  is  produced 
in  quantities  large  enough  to  make  hand  pollination  practicable 
must  be  determined  during  their  comparison  as  varieties.  It  has 
been  held  by  many  horticulturists  since  the  time  of  T.  A.  Knight 
(60)  that  varieties  which  did  not  bloom  readily  could  be  stimulated 
into  fruiting  by  removing  the  soil  from  the  underground  stems,  or 
otherwise  preventing  the  production  of  tubers.  This  does  not  seem 
to  be  true  at  present  with  American  varieties,  for  with  ten  different 
varieties  in  Connecticut  and  with  five  in  Illinois,  we  obtained  by 
this  method  no  natural  seed  balls,  and  by  microscopical  examination 
found  no  seeming  increase  in  production  of  viable  pollen.  At  least, 
we  might  conclude  that  the  reaction  to  this  means  is  not  certain 
enough  to  be  of  great  value  to  the  breeder,  and  seed  producing  va- 
rieties must  be  selected  which  come  nearest  to  the  ideal  in  the  char- 
acters needed.  Some  hybridists  select  parent  varieties  of  similar 
type  with  the  idea  of  improving  qualities  already  obtained,  while 
others  cross  widely  divergent  types,  with  the  hope  of  obtaining  a 
smaller  percentage  of  seedlings  with  much  better  characteristics. 
Doubtless  both  methods  are  necessary,  if  it  is  certain  in  all  cases 
that  there  are  eminently  desirable  characters  in  the  types  used. 

Having  selected  the  varieties  with  which  to  work,  it  is  of  doubt- 
ful value  to  use  any  of  the  old-time  horticultural  methods, — such 
as  over  supply  of  food  materials, — to  induce  variation.  We  may  in 
the  future  learn  to  use  artificial  means  to  produce  mutations,  but 
the  "plus"  fluctuations  induced  by  food  supply  are  probably  abso- 
lutely valueless  when  we  are  about  to  resort  to  sexual  reproduction 


392 


BULLETIN  No.  127. 


[August. 


in  the  origination  of  new  types.  But,  even  if  artificially  produced 
fluctuations  were  heritable,  there  would  be  no  necessity  for  their 
production;  for,  owing  to  the  hybrid  character  of  the  greater 
number  of  potato  varieties — or  for  other  reasons — the  natural 
variation  of  seedlings  is  very  great,  even  when  they  are  the  product 
of  crosses  within  the  variety.  Foreign  varieties  may  very  properly 
be  grown  until  they  are  fully  acclimated;  that  is,  until  the  varie- 
ties are  growing  with  full  vigor.  During  the  first  year  or  two  such 
varieties  seldom  flower ;  and  even  if.  they  do,  the  flowers  fall  more 
quickly  than  they  do  with  vigorous  plants,  and  hybridization  is  ef- 
fected with  difficulty. 

There  is  also  some  doubt  as  to  the  value  of  bud  variations,  but 
pending  further  investigations,  we  should  watch  for  any  such  oc- 
currences. Data  soon  to  be  published  by  the  writer  seem  to  indicate 
that  progressive  mutations,  that  is,  the  appearance  of  an  entirely 
new  character,  rarely  and  possibly  never,  occur.  Bud  variations 
are  in  nearly  all  cases  merely  the  loss  of  a  dominant  character  leav- 
ing the  recessive  allelomorph  to  appear.  Such  variations  are  not 
likely  to  be  of  great  economic  value. 

The  selection  of  individual  plants  to  be  crossed  is  still  a  matter 
of  personal  opinion  and  experiment.  While  we  may  not  believe  in 
the  heritability  of  vigor  occurring  as  a  fluctuation  within  a  variety ; 
still  the  greater  ease  of  making  crosses  between  vigorous  plants  is  a 
sufficient  reason  for  their  selection  as  mother  plants.  The  latter  is 
due  to  the  greater  probability  of  their  retaining  the  seed  ball  to  its 
maturity. 

Girard  selected  plants  having  the  most  luxuriant  vegetation, 
and  according  to  T.  A.  Scarlett  (88),  the  same  method  is  practiced 
in  Scotland.  We  have  found  that  there  is  a  great  difference  in 
varieties,  as  regards  the  value  of  luxuriant  vegetation  as  a  guide 
in  selecting  high  yielding  plants.  Large  vines  versus  medium  vines 
gave  fair  results  MI  most  cases ;  but  in  some  varieties  as  Manistee, 
large  vines  rather  indicated  that  excessive  vegetative  growth  was 
opposed  to  maximum  tuber  formation. 

TABLE  2.    SELECTION  OF  HIGH  YIELDING  PLANTS  BY  SIZE 


Variety. 

Average  vine  production 
in  ounces. 

No.  counted 
of  each. 

I^arge  vines. 

Medium  vines. 

Pink  Gem  

21.5 
24.1 
22.1 
16.0 
16.6 

14.25 
19.3 
20.0 
16.1 
16.9 

50 
50 
10 
10 
10 

Sir  Walter  Raleigh  
Carman  No.  3  

Early  Ohio  

IMPROVEMENT  OF  THE  POTATO.  •     393 

There  is  no  constant  difference  due  to  selection  of  plants  with 
a  single  stem  and  those  which  branch  just  below  and  just  above  the 
ground,  providing  they  are  equal  in  top  weight  and  that  it  is  cer- 
tain that  the  branched  selections  are  single  plants.  There  appears, 
however,  to  be  an  optimum  shade  of  color  in  vines,  constant  with 
the  variety,  which  is  correlative  with,  or  a  result  of  vigor  in  the 
plant.  Lighter  colors  gave  fewer  potatoes  although  these  were  of 
good  size,  while  darker  colors  either  gave  no  set  of  tubers  or  a 
large  set  of  very  small  tubers.  The  latter  condition  sometimes 
seems  to  be  due  to  a  very  late  setting  of  tubers  in  late  varieties, 
leaving  too  short  a  season  for  the  tubers  to  mature. 

The  actual  crossing  of  the  plants  selected  is  a  simple  matter. 
The  corolla  and  stamens  of  the  selected  blossom  of  the  mother 
plant  should  be  cut  away  before  it  is  fully  developed,  and  the  blos- 
som then  bagged  with  a  small  waxed  paper  bag.  When  the  stigma 
is  receptive  (sticky),  dust  on  the  pollen  collected  from  the  "sire" 
plant  with  a  camel's  hair  brush.  This  pollination  should  be  repeated 
on  two  successive  days,  if  the  pistil  has  not  fallen.  It  is  better  to 
limit  the  fruits  of  the  mother  plant  to  two,  but  several  flowers 
should  be  pollinated  in  order  to  stimulate  growth  in  the  peduncle 
of  the  cyme.  When  the  fruit  has  begun  to  form,  remove  the  bag 
to  allow  free  access  to  air  and  light.  When  the  fruits  are  ripe,  they 
are  gathered  and  allowed  to  dry.  It  is  better  for  their  viability  to 
squeeze  out,  clean  and  dry  the  seed,  rather  than  allow  them  to  stay 
all  winter  in  the  berries  where  there  is  an  opportunity  for  decay. 


FIG.  4.    IRREGULAR  CYME  OF  POTATO   FLOWERS.    ONE  READY  FOR  POLLINATION. 


394  BULLETIN  No.  127.  [August, 

The  seed  is  planted  in  a  hot  house  in  February  and  transplanted 
twice  before  planting  in  the  open  after  danger  of  frost  is  over. 
Fraser  (37  p.  174)  believes  the  old  idea  of  this  first  year  crop  con- 
sisting of  small  tubers  does  not  always  hold  and  states  that  a 
tuber  weighing  over  seven  ounces  has  been  grown  the  first  year. 
He  says,  "The  Burbank  potato  was  full  size  the  first  year  it  was 
grown  from  seed,  and  many  breeders  feel  that  unless  the  tubers  are 
of  edible  size  the  first  year  that  they  are  not  likely  to  be  worth  fur- 
ther care."  Girard  (45)  also  states  that  with  proper  cultivation, 
seedlings  will  produce  marketable  tubers  in  one  or  two  years. 

I  have  seldom  seen  a  marketable  tuber  produced  by  even  a  two 
year  seedling,  and  think  that  such  results  must  be  unusual.  The 
vines  certainly  often  reach  full  size  the  first  year,  but  the  growth  is ' 
almost  entirely  vegetative  with  very  little  matter  stored  in  the 
form  of  tubers.  The  vines  producing  the  larger  tubers  seldom  pro- 
duce a  large  number,  and  I  have  been  told  by  several  reliable  breed- 
ers that  they  prefer, — the  first  year  as  well  as  subsequent  years, — 
to  select  the  vines  having  the  largest  number  of  tubers.  And  while 
there  are  no  comparative  data,  the  use  of  the  plant  as  a  whole  as  a 
selective  unit  appears  the  more  reasonable.  The  great  majority  of 
the  seedlings  produce  tubers  of  only  one  to  fifty  grams  weight  the 
first  year  and  require  three  years  to  reach  their  full  size.  It  is  also 
noticeable  that  the  typical  shape  of  the  strain  is  not  generally 
shown  the  first  year,  the  tubers  at  this  time  generally  being  round 
in  shape. 

PRECAUTIONS  IN  COMPARATIVE  TESTS 

After  the  first  year  the  elimination  of  the  unfit  begins.  The 
tubers  from  the  ^year  before  are  compared  in  the  garden  in  short 
rows  and  as  elimination  goes  on  the  best  are  given  field  trials.  In 
carrying  out  all  field  and  garden  comparison  tests,  there  are  a  great 
number  of  factors  which  have  an  influence  upon  growth,  and  which, 
as  far  as  possible,  must  be  taken  into  account;  for  a  field  test  at 
best  has  a  large  experimental  error  and  the  error  with  potatoes  is 
probably  larger  than  with  any  of  the  seed  propagated  annuals. 

The  more  common  operations  of  all  field  experiments  which 
first  come  to  mind  and  which  scarcely  would  be  neglected  in  the 
comparison,  are  absolute  uniformity  in  the  time  of  planting,  num- 
ber of  times  and  methods  of  cultivation  and  spraying,  kind  and 
amount  of  fertilizer,  and  time  of  harvesting  after  dividing  the  va- 
rieties into  early,  medium  and  late  maturing.  There  are  a  number 
of  other  points  which  have  been  neglected  in  far  too  many  potato 


IMPROVEMENT  OF  THE  POTATO.  395 

investigations.  A  common  error,  as  Thorne  has  pointed  out  (97), 
is  in  disregarding  the  type  and  typography  of  the  soil.  The  soil 
should  be  as  uniform  as  possible,  preferably  of  sedentary  origin, 
and  previous  to  its  experimental  use,  should  have  been  fertilized 
and  cropped  in  exactly  the  same  manner.  The  land  should  be 
slightly  rolling  and  the  potato  rows  should  run  up  and  down  the 
declivity  so  that  the  comparison  of  the  whole  rows  is  perfectly  fair. 
Water  is  a  very  important  factor  in  potato  growing,  and  small 
depressions  in  flat  lands  receive  an  unequal  portion  of  the  surface 
drainage  which  vitiates  the  results. 

E.  Pagnoul  (77)  attributed  the  large  yield  of  potatoes  in  sea- 
sons when  the  total  hours  of  sunshine  were  large,  to  the  effect  of 
light  on  elaborating  starch.  His  results  may  be  slightly  distorted 
as  he  reports  only  a  portion  of  the  conditions  which  enter  into  his 
experimental  error,  but  results  as  reported  gave  a  ratio  of  approxi- 
mately 1 15  :n  for  plants  under  darkened  glass,  clear  glass  and  open 
air  respectively.  Therefore  precaution  should  be  taken  concerning 
all  shade. 

Results  from  numerous  experiments,  among  the  most  accurate 
of  which  are  those  of  Maw  (74)  and  Plumb  (82),  have  shown  that 
much  care  must  be  taken  to  have  equal  weight  of  seed  planted,  for 
other  conditions  being  equal,  the  yield  of  tubers  increases  directly 
with  the  weight  of  the  seed  piece  although  not  exactly  proportional. 

Arthur  (2,  3)  and  others  have  pointed  out  a  difference  in  yield 
owing  to  the  difference  in  age  and  vigor  of  eyes  sprouted  before 
planting.  Wilting  tubers  up  to  a  loss  of  moisture  of  20  percent  also 
increased  growth.  He  advances  the  proposition  that :  "Whatever 
increases  rate  of  growth  at  the  beginning,  increases  yield."  Finally 
Gilmore  (44)  has  shown  that  depth  of  planting  certainly  affects  the 
quality  and  on  certain  soils  the  yield;  while  Clinton  (16)  suggests 
that  it  may  also  cause 'a  difference  in  time  of  infection  with  Phy- 
tophthora  infest ans. 

These  factors  can  probably  never  all  be  controlled  in  the  same 
experiment  but  they  should  all  be  kept  in  mind,  and  all  reasonable 
effort  made  to  lessen  errors  due  to  them  in  comparative  tests. 

CORRELATIONS 

Many  so-called  correlations  of  characters  have  been  observed 
by  different  investigators.  These  correlations  are  said  to  be  some- 
times 'very  marked,  and  of  great  value  in  making  selection 
where  one  of  the  correlated  characters  is  easier  to  select  from 
than  the  other.  The  physiological  reasons  for  many  of  these  ef- 


396  BULLETIN  No.  127.  [August, 

fects  are  obscure,  and  there  appears  to  be  no  certain  way  of  dis- 
tinguishing between  what  might  be  called  real  correlations,  which 
are  probably  to  a  greater  or  less  degree  effects  from  the  same  in- 
ternal cause,  or  where  two  characters  are  inherited  as  a  single  unit : 
and  false  correlations  in  which  one  is  the  cause  and  the  other  the 
effect,  or  in  which  both  characters  vary  as  the  result  of  some  ex- 
ternal stimulus.  In  practical  work  either  type  may  become  a  help 
in  its  prosecution,  but  in  studying  problems  of  heredity,  inability  to 
distinguish  the  type  often  leads  to  great  confusion.  Space  cannot 
be  taken  to  comment  upon  these  observations  except  to  make  the 
statement  that  it  has  been  the  writer's  experience  that  the  degree  of 
correlation  of  any  characters  which  he  has  observed,  is  extremely 
variable  with  different  varieties,  on  diverse  types  of  soil,  and  in  dis- 
similar seasons. 

With  regard  to  the  production  of  plants,  Arthur  (2)  in  an 
elaborate  investigation  found  that  the  number  of  stalks  is  very 
slightly  if  at  all  related  to  the  number  of  eyes  upon  the  seed  piece, 
provided  pieces  of  equal  weight  are  used.  The  number  of  stalks, 
however,  increases  directly  with  the  weight  of  the  seed  piece;  and 
with  the  number  of  stalks  varies  directly  the  number  of  tubers  and 
their  total  weight  in  the  produce.  He  also  and  later  Wollny  (112) 
state  that  the  eyes  of  large  tubers  produce  stems  of  a  sturdier 
growth. 

Liebscher  (66)  states  that  thin  stemmed  plants  produce  small 
tubers  and  that  plants  with  fine  stems  produce  many  small  tubers. 

There  seems  to  be  no  constant  relationship  between  colors  of 
tubers  and  of  blossoms  or  between  dark  skinned  tubers  and  dark 
vines,  but  Liebscher  (66)  found  that  profuse  blossoming  points  to 
late  ripening,  and>  heavy  seed  setting  to  small  tuber  formation.  The 
latter  statement  has  been  a  general  belief  but  Fraser  (37)  states 
that  in  his  experience  many  of  the  heaviest  yielding  varieties  at 
least  bloom  freely.  Liebscher  believed  seed  and  tuber  production 
to  be  physiologically  opposed.  Fruwirth  (43  v.  3  p.  10)  states  that 
Dalkowsky  is  of  the  opinion  that  strong  power  of  seed  production 
is  also  correlated  with  ability  to  resist  disease. 

Osterspey  (76)  found  in  early  varieties  less  foliage  than  in  late 
varieties;  and  within  a  variety,  in  both  early  and  late  varieties, 
there  was  a  relation  between  number  of  tubers  and  number  of 
stalks. 

Fischer  (32)  found  that  flat-round  tubers  were  richer  in  starch 
and  produced  less  massive  plants;  while  long-cylindrical  tubers 
were  poorer  in  starch  and  produced  large  straggling  foliage.  Fru- 


ipoS.]  IMPROVEMENT  OF  THE  POTATO.  397 

wirth  (41),  in  three  years'  observations  with  both  early  and  late 
varieties  found  a  relation  between  yield  and  the  following  charac- 
ers:  Flat  shape,  number  of  stalks  per  plant,  length  of  growing 
period,  height  of  plants  and  number  of  tubers  per  plant.  He  also 
states  that  the  greater  the  number  of  stalks  from  a  plant,  the 
thinner  are  the  stalks. 

Some  of  these  correlations  may  help  materially  in  eliminating 
some  of  the  undesirable  plants  from  the  progeny  of  crosses  from 
which  we  are  trying  to  build  up  new  varieties.  There  may  also  be 
many  pairs  of  characters  with  high  percentage  correlation  which 
have  not  yet  been  noticed  but  which  will  be  brought  out  with 
further  statistical  studies.  It  is  doubtful,  however,  if  many  of 
these  characters  which  appear  to  be  related  in  certain  varieties, 
are  to  be  regarded  as  real  correlations  characteristic  of  the  species. 
Reasoning  from  statistical  studies  of  the  writer  on  maize  and  sugar 
beets,  which  may  or  may  not  be  analogous,  it  would  seem  that  cor- 
relations which  are  likely  to  be  of  most  practical  value  in  making 
selections  will  probably  be  found  in  very  narrow  blood  lines  (ele- 
mentary species?).  For  example,  in  ear-to-the-row  tests  of  dent 
maize  there  was  planted  an  ear  with  a  peculiarly  shaped  tip.  This 
ear  yielded  very  highly,  and  of  its  progeny  when  grown  and  their 
yield  compared,  in  nearly  every  case,  those  were  found  to  average 
highest  whose  mothers  had  this  peculiar  -tip. 

In  hybridization,  pairs  of  characters  may  be  found  which  are 
inherited  as  a  single  character.  When  both  characters  are  desir- 
able, this  would  be  a  decided  help,  but  when  one  character  is  unde- 
sirable, there  is  only  the  consolation  of  knowing  the  difficulty  of 
finding  exceptions  to  the  rule.  Johannsen  (58)  states  however 
that,  "Crossing  is  the  means  of  breaking  the  correlation/' 

In  selection,  those  correlations  are  of  greatest  value  which  al- 
low us  to  eliminate  plants  through  correlations  of  characters  in  the 
young  vines,  with  characters  in  the  tubers.  It  is  doubtful,  however, 
whether  weak  correlations  should  be  used  in  originating  varieties. 
They  are  probably  of  practical  value  only  when  the  life  history  of 
the  variety  is  known. 


BULLETIN  No.  127.  [August, 

5.  INHERITANCE  OF  CHARACTERS  IN  TUBER 
SELECTION 

THEORY 

We  do  not  mean  by  this  term  the  inheritance  of  the  characters 
in  future  sexual  crosses,  but  the  transmission  of  selected  variations 
from  year  to  year  by  tubers.  A  consideration  of  this  question  is 
of  practical  importance  to  the  potato  grower.  The  potato  breeder 
may  still  continue  to  make  crosses  and  originate  varieties,  but  in 
such  work  he  is  and  must  be  a  specialist.  His  work  can  never  be 
undertaken  with  profit  by  the  average  grower,  to  improve  his  stock. 
On  the  other  hand,  if  there  is  a  possibility  of  selecting  and  propa- 
gating favorable  fluctuating  variations  and  their  accumulation  for 
the  betterment  of  the  variety,  such  work  can  be  undertaken  with 
success  and  profit  by  the  farmer. 

It  is  common  knowledge  that  during  the  first  few  years  the 
progeny  of  a  sexual  cross  in  potatoes  is  quite  variable.  These 
variations  may  be  arbitrarily  divided  into  two  classes :  First,  those 
variations  that  seem  to  be  due  directly  to  slight  differences  in  en- 
vironment, such  as  shape,  size  and  yield  of  tubers,  and  vigor  of 
growth  and  amount  of  foliage  in  plants;  second,  variations  that 
are  much  rarer  and  that  seem  to  be  of  a  more  nearly  botanical  char- 
acter as  those  of  color  tubers,  length  of  life  of  plant,  and  amount 
of  blossoms  and  production  of  seed.  Variations,  in  the  after  life 
of  the  variety  are  said  to  become  less  common,  that  is,  the  type  of 
the  variety  is  said  to  become  fixed.  This  appears  to  be  true  from 
general  observations  of  potato  seedlings,  and  it  might  partially  be 
explained  by  the  fact  that  each  year  the  plants  are  subject  to  rigid 
selection  to  a  certain  type.  //  these  fluctuations  are  transmitted, 
the  plants  dealt  with  in  subsequent  years  are  a  selected  and  not  a 
general  race.  But  when  unselected  it  is  probable  that  there  is 
a  lessening  variability  with  advancing  age,  even  when  the  physio- 
logical vigor  of  compared  plants  is  kept  the  same.  Vernon  (99  p. 
184)  showed  conclusively  that  for  low  forms  of  animals  as  the  sea 
urchin  that  the  "Permanent  effect  of  environment  on  the  growth  of 
a  developing  organism  diminishes  rapidly  and  regularly  from  the 
time  of  impregnation  onwards."  A  little  later  De  Vries  (26)  enun- 
ciated practically  the  same  law  for  plants.  He  concludes:  i.  The 
younger  the  plant,  the  greater  is  the  influence  of  external  condi- 
tions on  its  variability.  2.  The  nutrition  of  the  seed  when  develop- 
ing on  the  mother  plant  has  (at  least  very  often)  a  greater  influ- 
ence on  the  variability  than  during  germination  and  growth. 


IMPROVEMENT  OF  THE  POTATO.  399 

Hence  if  we  consider  a  potato  variety  as  a  perennial  individual, 
though  divided,  we  may  conclude  that  following  these  laws  the 
variability  lessens  as  the  variety  becomes  older. 

Admitting  this  law  to  be  sufficient  reason  for  lessened  variation 
in  the  variety  as  it  ages;  there  is  still  variation,  and  as  Bailey  (4) 
has  shown  considerable  variation,  both  continuous  and  discontinu- 
ous, or  with  De  Vriesian  names,  both  fluctuations  and  mutations. 
In  the  progress  of  evolution,  such  variations  must  have  been  suf- 
ficient either  as  mutations  or  as  accumulated  fluctuations  to  have 
created  varieties  and  even  species.  In  no  other  way  could  the 
numerous  species  and  varieties  of  the  asexually  propagated  fungi 
have  originated,  as  well  as  numerous  varieties  of  higher  plants  of 
various  families,  as  sugar  cane,  banana,  weeping  willow,  sweet  po- 
tato, olive,  fig  and  date  which  seldom  or  never  are  propagated  by 
seeds.  But  as  most  biologists  now  accept  the  doctrine  of  discontin- 
uous evolution  we  cannot  a  priori  conclude  that  partial  fluctuations 
(using  the  terms  described  below)  are  inherited  even  in  the  tem- 
porary Galtonian  way  in  which  individual  fluctuations  are  inher- 
ited. De  Vries  (27)  divides  fluctuations  into  two  heads  which  he 
says  "obey  quite  the  same  laws,"  but  which  with  respect  to  ques- 
tions of  heredity  should  be  carefully  separated.  "They  are  desig- 
nated by  the  terms  'individual'  and  'partial'  fluctuation.  Individual 
variability  indicates  the  differences  between  individuals,  while  par- 
tial variability  is  limited  to  the  deviations  shown  by  the  parts  of 
one  organism  from  the  average  stature."  Fluctuations,  he  says, 
take  place  in  only  two  directions,  the  increase  or  decrease  of  what 
characters  are  already  available,  and  in  this  way  are  fundamentally 
different  from  mutations  which  take  place  in  all  directions,  and  if 
progressive  produce  new  characters.  He  concludes  that  partial  fluc- 
tuations are  usually  far  smaller  than  individual  and  partial  fluctua- 
tion together,  and  that  partial  variations  do  not  appear  to  offer  im- 
portant material  for  selection.*  Multiplication  by  buds,  however, 
of  high  extremes  of  individual  fluctuation,  he  says,  is  what  the 
breeder  desires  to  obtain. 

From  De  Vries'  work,  we  might  conclude  that  although  partial 
fluctuations  obey  the  same  laws  as  individual  fluctuations,  there  is 
not  a  great  chance  for  improvement  through  their  selection,  because 
of  their  narrowness.  Theoretically  the  fluctuations  of  the  whole  of 
any  variety  of  potatoes  belong  to  this  class.  Still  the  variability 

*De  Vries,  however,  admits  the  possibility  of  the  commercial  value  of  the  selection  of  par- 
tial variations,  when  he  says  (P.  766):  "Potatoes  for  the  factory  have  even  been  selected  for 
their  amount  of  starch,  and  in  this  case  at  least,  fluctuating-  variability  has  played  a  very  im- 
portant part  in  the  improvement  of  the  race."  This  is  an  admission  of  something-  that  cannot 
be  regarded  as  an  undisputed  fact.— E.  M  E. 


400  BULLETIN  No.  127.  [August, 

should  be  greater  in  the  potato  than  in  parts  of  perennial  plants 
from  a  single  rootstock, — from  the  latter  class  of  which  De  Vries 
obtained  a  great  deal  of  his  data, — on  account  of  greater  diversity 
of  environmental  forces.  The  variation  here  ought  to  be  analogous 
to  the  individual  fluctuations  of  the  fungi,  or  asexual  animals  which 
have  the  power  of  obtaining  food  in  different  places  and  of  being 
surrounded  by  diverse  conditions. 

A  study  of  the  actual  amount  of  difference  of  fluctuating  vari- 
ability in  asexual  and  sexual  reproduction  has  been  made  by  Pear- 
son (80),  who  also  makes  use  of  Warren's  (102)  work  on  parthen- 
ogenetic  reproduction  in  Daphnia.  Their  work  makes  use  of  data 
from  both  animals  and  plants  which  might  be  criticized  as  not  be- 
ing strictly  comparable,  although  most  great  biological  laws  have 
thus  far  seemed  to  apply  to  both  animals  and  plants. 

His  first  proposition  is  that  selecting  one  parent  reduces  the 
variability  of  the  race  by  only  about  5  percent  while  selecting  both 
parents  reduces  it  about  10  percent,  and  this  is  almost  the  limit  of 
reduction  even  if  the  whole  back  ancestry  be  selected.  The  varia- 
tion then  taking  place  is,  of  course,  from  the  new  type  and  not  from 
the  unselected  type. 

This  proposition  if  true  for  such  reproduction*  as  there  is  in 
potatoes,  would  show  the  probable  amount  of  reduction  of  varia- 
bility which  there  is  in  the  established  variety  after  it  has  been 
selected  to  type  for  several  years  and  then  placed  on  the  market, 
leaving  out  of  consideration  the  lessened  variation  due  to  greater 
age  in  the  variety. 

The  next  point  is  that  the  individualf  variability  in  a  fluctuating 
character  after  a  bi-sexual  union  is  not  greatly  less  than  the  varia- 
bility of  the  race.  As  an  example,  is  taken  the  number  of  stigmatic 
bands  on  the  capsules  of  Shirley  poppies.  The  racial  variability  is 
1.885  bands,  the  individual  variability  based  on  300  plants  is 
.8518x1.885,  or  a  reduction  of  15  percent.  Again,  the  racial  varia- 
bility of  the  number  of  leaflets  on  the  compound  leaf  of  the  ash  was 
found  by  examining  two  hundred  trees  to  be  1.976;  the  partial 
variability  is  .9181x1.976  or  a  reduction  of  only  8  percent.*  * 

The  last  point  is  made  on  the  variability  of  mothers  and  daugh- 
ters in  the  purely  asexual  reproduction  of  Daphnia.  The  variability 
of  the  mothers  for  a  certain  character  was  2.221,  for  their  daugh- 

*This  fact  should  be  true  at  least  for  selectioti  from  crosses. 

tPearson  does  not  distinguish  here  as  does  De  Vries  between  indidividual  and  partial  fluct- 
uations. 

**The  writer  does  not  subscribe  to  all  of  Pearson's  conclusions  on  homotyphosis.  There 
are,  however,  certain  fluctuating  characters  where  the  individual  variation  is  probably  but 
little  less  than  that  of  the  race. 


1908.]  IMPROVEMENT  OF  THE  POTATO.  401 

ters  2.950;  for  the  array  of  daughters  due  to  a  mother  of  given 
character,,  an  average  of  2.610.  Even  after  considering  that  moth- 
ers are  a  selection  and  not  a  race,  the  following  conclusions  are 
drawn : 

,(i)  "In  asexual  reproduction  an  individual  does  not  produce  a  facsimile 
of  itself,  and  the  variability  of  its  offspring  is  not  immensely  reduced  below  the 
variability  of  the  race. 

(2)  The  asexual   individual  has   offspring  exhibiting   regression,   just  like 
the  sexually  reproductive  individual.     Its  offspring  tends  to  regress   from  the 
individual  to  the  race  type. 

(3)  With  high  probability  but  not  definitely,  the  asexual  individual  repre- 
sents the  mid-parent  (i),  i.  e.  .466  and  .619  are  well  within  the  probable  errros 
of  the  values  .424  and  .600,  which  we  have  found  (Grammar  of  science  p.  471) 
for  the  correlation   and  regression  of  the   mid-parent  in  the  case  of  the  bi- 
parental  inheritance." 

Summing  up  the  whole  case,  he  says : 

(1)  "Whatever  be  the  physiological  function  of  the  sex  in  evolution,  it  is 
not  the  production  of  greater  variability." 

(Note)  This  does  not  mean  that  sex  is  not  a  great  factor  in 
producing  a  great  variety  of  forms  by  combinations  of  existing 
diverse  characters,  but  these  differences  must  exist  in  the  parents 
or  previous  ancestry  of  the  individuals  producing  this  combination. 

(2)  "The  variability  of  the  individual  makes  itself  felt  not  only  in  the  bi- 
parental  reproduction  but  in  autogamic  and  parthenogenetic  reproduction,  and 
further  in  the  undifferentiated  like  parts  of  the  same  individual. 

(3)  Whatever  amount  of  selection  has  taken  place,  there  seems  no  possi- 
bility of -reducing  variability  beyond  some  10  percent  or  II  percent." 

From  the  evidence  given  above,  it  seems  reasonable  for  us  to 
make  the  following  conclusions  as  a  working  basis  for  our  own 
problems.  First,  that  there  is  fluctuating  variation  in  asexually 
propagated  vegetation  which  when  reduced  to  a  basis  comparable 
to  sexually  propagated  plants,  is  not  to  a  great  degree  inferior.  Sec- 
ond, that  decreasing  variability  in  a  potato  variety  need  not  be  due 
to  a  fixation  of  type  which  presupposes  an  inheritance  of  fluctua- 
tio*ns.  It  may  be  explained  by  the  decreased  reaction  to  environ- 
ment of  an  aging  individual.  Third,  that,  if  partial  fluctuations 
obey  the  same  laws  as  other  fluctuations,  types  may  be  changed  by 
their  selection ;  and  this  selection  reduces  the  variation  of  the  char- 
acter in  the  neighborhood  of  10  percent. 

Our  whole  problem  is  reduced  to  the  question  whether  types 
may  or  may  not  be  changed  by  the  selection  of  fluctuations.  If 
types  may  be  changed  by  the  selection  of  individual  fluctuations, 
they  may  likewise  be  changed  by  the  selection  of  partial  fluctuations. 
Until  recently  an  affirmative  answer  to  this  theorem  would  not  have 


402  BULLETIN  No.  127.  [August, 

been  questioned.  All  of  our  conclusions,  however,  have  been  based 
upon  the  supposition  that  the  data  obtained  in  experiments  with 
fluctuations,  were  obtained  from  homogeneous  material.  Johann- 
sen's  (58  a,  b)  work  has  thrown  into  considerable  doubt  the  homo- 
geneity of  natural  populations.  He  has,  moreover,  concluded  that 
the  selection  of  fluctuations  has  nothing  to  do  with  the  improvement 
of  a  race.  Probably  no  other  conclusion  of  recent  times  is  so  im- 
portant to  plant  breeders.  The  work  should  certainly  be  duplicated 
along  as  many  lines  as  possible;  for  its  corroboration  would  not 
only  sound  the  death  knell  of  methods  of  improvements  by  the  se- 
lection of  partial  fluctuations,  but  would  entirely  change  our  con- 
ception of  procedure  in  other  breeding  operations. 

Johannsen's  experiments  were  made  upon  typical  fluctuating 
characters,  such  as  weight  and  length  of  seeds.  The  plants  used 
were  species,  like  beans,  that  could  be  self-fertilized  during  suc- 
cessive generations.  All  of  the  descendants  of  a  single  plant,  aris- 
ing by  self-fertilization,  he  speaks  of  as  a  "pure  line."  The  mem- 
bers of  a  pure  line  were  distributed  normally  around  a  modal  or 
type  value  in  the  case  of  each  character  considered.  Likewise,  all 
seeds  from  plants  of  the  same  variety,  made  up  of  a  large  number 
of  pure  lines,  showed  a  normal  variability.  Some  of  the  modal 
values  of  the  pure  lines  were  very  close  to  the  modal  value  of  the 
variety,  while  in  other  pure  lines  the  modes  were  quite  different 
from  it.  When  any  individual,  differing  widely  from  the  mean 
value  of  its  pure  line,  was  selected  for  propagation,  its  offspring 
showed  almost  a  complete  regression  to  the  type  of  its  particular 
line ;  but  showed  no  regression  whatever  to  the  type  of  the  variety. 
He  concludes,  then,  that  a  natural  variety  consists  of  a  larger 
or  smaller  number  of  distinct  types,  each  type  having  a  distinct 
modal  value  for  'particular  fluctuating  character.  These  distinct 
types  he  calls  "biotypes."  Only  by  mutation  or  some  rearrange- 
ment of  characters  can  a  pure  line  come  to  contain  more  than  one 
biotype.  If  such  a  phenomenon  takes  place,  the  new  biotype  dm 
be  isolated,  and  remains  true  until  another  mutation  or  rearrange- 
ment takes  place.  It  is  quite  clear  that  the  only  role  of  selection  is 
to  more  or  less  completely  isolate  the  different  biotypes  of  a  variety. 

Johannsen  leaves  out  of  consideration  forms  of  vegetative  prop- 
agation; though  for  what  reason  I  cannot  understand.  Tuber  re- 
productions in  potatoes  is  a  form  of  reproduction  in  a  pure  line.  If 
these  conclusions  are  wholly  warranted, — and  Johannsen's  work  is 
extremely  careful, — no  improvement  can  be  made  by  selecting  plus 
fluctuations  in  potatoes,  except  upon  the  intervention  of  mutative 


1908.] 


IMPROVEMENT  OF  THE  POTATO. 


403 


changes.  That  mutative  changes  do  take  place,  we  are  certain ;  but 
nothing  is  known  of  their  character  or  frequency.  I  believe  that  po- 
tatoes are  very  good  material  with  which  to  throw  some  light  upon 
the  subject.  It  is  only  just  to  note,  however,  that  the  experimental 
work  reported  in  this  paper  was  planned  and  executed  before  Jo- 
hannsen  reported  his  experiments.  The  experiment  has  now  been 
revised  to  better  fit  the  problem. 

EXPERIMENTAL  EVIDENCE 

Believing  that  the  practical  experiments  in  tuber  selection  are 
of  some  value,  we  have  made  a  study  of  the  reported  results. 

As  early  as  1860  Hellriegel  (55),  from  a  three  years'  experi- 
ment, came  to  the  conclusion  that  it  is  not  possible  to  improve  a 
variety  of  potatoes  in  starch  content  by  the  selection  of  tubers  hav- 
ing a  high  specific  gravity.  His  experiments  gave  the  following 
starch  contents  from  selections  of  tubers  of  high  and  low  specific 
gravity : 


1858 

1859 

1860 

From 

mothers  of  hig-h  specific 
"    low 

gravity  . 

1.0789 
1.0776 

1.0907 
1.0888 

1.0720 
1.0701 

It  can  be  seen  that  the  slight  difference  shown  here  might  easily 
be  due  to  experimental  error  and  that  there  is  no  cumulative  effect 
due  to  the  selection. 

Franz  (36)  in  1878  concluded  that  from  his  experience  and 
from  general  farm  practice  that  varieties  at  least  could  be  kept  up 
in  vigor  by  the  selection  of  the  seed. 

Emery  (30)  took  a  step  in  advance  in  method  and  used  one 
hundred  tubers  from  poorest  hills  as  compared  with  one  hundred 
tubers  of  the  same  weight  from  the  best  hills.  His  results  were  ir- 
regular and  he  came  to  no  conclusion. 

Wollny  (no)  took  a  further  step  toward  lessening  experimen- 
tal error,  and  used  only  tubers  of  the  same  weight,  but  he  concluded 
that  selection  of  tubers  with  a  high  specific  gravity  shows  no  defi- 
nite influence  upon  the  progeny  either  in  quality  or  amount  of  yield. 

Later  Marek  (69)  opposed  these  conclusions.  His  work  is 
weak,  however,  from  the  fact  that  he  divided  his  tubers  into  dif- 
ferent sizes,  and  after  finding  that  the  heaviest  tubers  were  highest 
in  specific  gravity,  he  used  them  as  seed.  The  results  were  probably 
due  in  great  measure  to  the  heavier  seed  piece  used. 


404 


BULLETIN  No.  127. 


[August, 


Marek's  work  stimulated  Wollny  (113)  to  continue  his  inves- 
tigations. In  this  later  work  his  former  conclusions  were  modified. 
He  found  that  in  the  majority  of  cases  the  progeny  of  tubers  hav- 
ing a  high  specific  gravity  were  of  a  slightly  higher  specific  gravity 
than  those  descended  from  tubers  of  a  low  specific  gravity.  He  be- 
lieves, however,  that  it  is  very  doubtful  whether  any  effectual  im- 
provement of  the  value  or  yield  of  a  variety  could  take  place 
through  selection  of  tubers  of  high  specific  gravity.  Further  in 
Marek's*  final  report,  he  admits  practically  the  same  thing. 

Girard  (45,  46)  reached  the  same  conclusion  with  regard  to 
specific  gravity  with  the  use  of  five  varieties,  but  highly  recommends 
the  selection  of  high-yielding  plants  in  the  field  as  means  of  keeping 
up  the  yield  of  the  variety. 

Hebert  found  no  transmission  of  high  specific  gravity  with  a 
large  number  of  experiments  with  Richter's  Emperator. 

Wohltmann's  (107)  and  Thiele's  (96)  results  showed  that  the 
hereditary  transmission  of  starch  content  had  not  been  clearly 
proved. 

Goff  (49),  in  experiments  begun  in  New  York  in  1884  and 
continued  four  seasons,  found  that  the  yield  of  tubers  from  pro- 
ductive hills  was  greater  than  that  from  unproductive  hills,  but  that 
the  difference  in  yield  between  different  rows  of  selected  tubers  was 
often  as  great  as  the  difference  between  the  two  selections,  and 
even  this  might  be  entirely  due  to  the  fact  that  the  plantings  were 
all  made  from  single  eye  pieces,  which  were  larger  in  those  from 
productive  hills.  Realizing  the  error  in  planting  different  weight 
seed  pieces,  he  (50)  began  again  in  1899.  This  time  the  same 
number  of  tubers  and  of  cuttings  were  taken  and  the  combined 
weights  of  each  selection  were  made  the  same.  The  collected  re- 
sults were  as  follows : 


Variety. 

Old  long  Mercer. 

Snowflake. 

Productive 
hills. 

Unproductive 
hills. 

Productive 
hills. 

Unproductive 
hills. 

Total  No.  of  tubers 
produced,  in  2  yrs 

104 

68 

232 

195 

Total  wt.  in  02. 
produced  in  2  yrs  

64 

41 

332 

100 

*Marek,  E.,  Deut.  landw.  Presse  1895:274. 


jpoo1.]  IMPROVEMENT  OF  THE  POTATO.  405 

He  concludes  that  the  vigor  of  the  plant  may  be  maintained  and 
even  increased  by  selection ;  but  that  the  experiment  has  not  tended 
to  increase  the  yield  of  the  varieties  used,  for  the  reason,  he  says, 
of  the  continued  cutting  of  the  best  tubers. 

Bolley  (12)  has  for  a  number  of  years  carried  on  an  investiga- 
tion concerning  the  use  of  large  and  small  tubers  from  the  same 
hill.  Bud  end  pieces  of  equal  weight,  cut  to  one  eye  piece  were 
used,  and  all  details  of  the  experiment  very  accurately  controlled. 
From  three  years'  observations,  he  concludes  that:  "In  planting 
equal  weight  pieces  from  small  and  large  tubers  of  the  same  vine, 
there  will  not  be  a  sufficient  difference  in  favor  of  the  one  or  the 
other  size  of  potatoes  to  be  noticeable  under  farm  methods,  pro- 
vided all  are  normally  mature."  This  shows  that  selection  of  large 
potatoes  from  the  bin  will  not  necesssarily  do  anything  toward  im- 
proving the  crop.  He  concludes  also  from  his  general  observations 
on  his  stock,  that  variations  in  forms,  size,  roughness  of  skin,  mal- 
formations, number  of  tubers,  etc.,  are  produced  to  some  extent 
though  influenced  greatly  by  seasonal  conditions.  From  this  he 
concludes  that  selecting  from  high  yielding  plants  should  improve 
the  yield.  Later  ( 13),  he  reports  his  first  conclusions  to  be  justified 
by  more  data. 

Fruwirth  (43)  criticises  Bolley 's  work  stating  that  he  had 
found  that  large  tubers  were  more  likely  to  produce  large  tubers 
than  were  small  tubers  even  from  the  same  vine.  He  gives  but 
few  data  warranting  this  conclusion,  and  I  think  that  he  overlooks 
Bolley's  qualifying  statement  that  "all  must  be  normally  mature." 

In  1899,  Remy  (85)  saw  a  part  of  the  error*  in  the  work  of 
former  German  and  French  chemists  who  used  physical  methods 
for  determination  of  specific  gravity,  and  estimated  their  starch 
from  this  by  Maercker's  tables.  He  found  that  a  great  number  of 
the  tubers  had  hollows  in  their  centers  which  seriously  vitiated  his 
results.  With  the  idea  of  correcting  this  fault,  he  selected  good 
smooth  potatoes  weighing  about  2oog.  each  and  used  about  7<3g. 
from  the  bud  end  for  planting,  while  he  determined  the  starch 
gravimetrically  in  the  remainder  by  the  use  of  Fehling's  solution. 
The  results  for  1899  and  JQOO  show  no  definite  relations  between 
the  nature  of  the  seed  tubers  and  the  progeny  either  in  dry  matter 
or  in  starch  content.  This  is  the  most  exact  experiment  up  to  this 
time,  although  even  the  chemical  method  for  starch  determination 
leaves  much  to  be  desired.  The  starch  fluctuations  were  rather 
narrow,  however,  running  in  1898  seed  from  76.0  percent  to  81.6 
percent  calculated  to  the  dry  substance;  and  two  crops  are  hardly 
sufficient  to  settle  this  question. 

From  1899  to  1901  appeared  the  notable  contributions  of 
Fischer  (33,  34,  35)  to  this  subject.  He  showed  that  there  was 

*See  writer's  table  of  fluctuations  in  nitrogen  content  for  further  error. 


406 


BULLETIN  No.  127. 


[August. 


a  definite  relation  between  the  shape  of  tubers,  and  starch  content 
and  power  to  yield,  and  that  such  individual  characters  were  in  a 
great  measure  transmitted.  The  author  believed  that  he  was  war- 
ranted in  concluding  that  within  a  variety  and  under  like  conditions, 
flat-round  tubers  produce  those  richest  in  starch,  but  weakest  in 
yielding  power,  while  cylindrical-oblong  tubers  give  a  progeny  poor 
in  starch  content  but  of  greater  yield.  The  explanation  of  the  cor- 
relation between  starch  content  and  flat-round  shape  is  from  the 
following  facts.  The  zone  of  highest  content  (see  discussion  con- 
cerning quality)  in  the  potato  lies  next  to  the  outside  of  the  tuber. 
Other  things  being  equal  then,  the  tuber  having  the  largest  propor- 
tion of  outer  starch  zone  is  the  richest  in  starch.  This  is  satisfied 
by  the  flat-round  tuber. 

In  these  investigations  two  varieties  were  used  and  selections 
made  of  rather  small-flat-round  tubers  on  one  hand,  and  large- 
cylindrical-long  tubers  on  the  other.  The  former  showed  a  specific 
gravity  of  more  than  i.n  and  the  latter  less  than  i.io.  These 
specific  gravities  correspond  in  Maercker's  tables  to  more  than  20 
percent  of  starch  in  the  former  and  less  than  18  percent  in  the 
latter. 

The  results  were  as  follows : 


Variety. 

Group. 

Aver,  weight 
seed  tubers 
in  grams. 

Yield  in 
kilos 
per  hectare. 

Yield  kilos  per 
ha.  minus 
wt.  of  seed. 

Sachsische 
2wiebel 

Flat- 
round, 
rich  in 
starch. 

60.6 

21900 

19900 

C3'lindrical- 
long, 
poor  in 
starch. 

68.0 

22600 

20360 

Reichs- 
kanzler. 

Flat- 
round, 
rich  in 
starch. 

.47.4 

19900 

18340 

Cylindrical- 
long, 
poor  in 
starch. 

62.5 

25305 

23290 

1908.] 


IMPROVEMENT  OF  THE  POTATO. 


407 


In  the  year  1898  the  experiment  was  continued  in  order  to  see 
if  a  transmission  of  the  relationships  under  discussion  was  contin- 
ued. For  this  reason  both  forms  of  tubers  were  selected  from  each 
group  of  the  crop  of  1897,  giving  in  1898  the  following  results: 


Variety. 

Form  of  tubers 
planted  in 
1897. 

Form  of  tubers 
planted  in 
1898. 

Aver.  wt. 
of  seed 
tuber  in 

Yield  of 
tubers  in 
kilos 

Yield  of 
tubers  in 
kilos 
per  ha. 

grams. 

per  ha. 

of  seed. 

Sachsische 

Flat-round. 

Flat-  round  
Cyl.-long-  

40.0 
89.5 

18500 
21730 

17180 
18780 

Zwiebel 

Cylindrical- 

Flat-round  

40.0 

19840 

18520 

long* 

Cyl.-long*  .... 

70  0 

22080 

19700 

Reichs- 

Flat-round. 

Flat-round  
Cyl.-long  

43.0 
85.0 

22620 
25  HO 

21200 
22640 

kanzler. 

Cylindrical- 

Flat-round  

43.0 

24060 

22640 

long. 

Cyl.-long-  

74.0 

27970 

25530 

An  inspection  of  the  table  certainly  appears  to  show  an  inherit- 
ance of  yield  in  tubers  which  had  been  selected  the  year  before,  the 
most  notable  being  the  increase  of  yield  in  the  Reichskanzler  va- 
riety where  the  long  tubers  from  the  long  tubers  of  1897  show  such 
a  remarkable  gain  over  the  long  tubers  from  the  round  tubers  of 
1897,  even  though  the  seed  weight  of  the  latter  is  the  greater.  There 
are  no  final  results  on  the  starch  content  given.  In  his  collected 
works  (32)  he  states  that  a  rise  in  starch  content  does  follow  se- 
lection of  starch  when  determined  by  exact  chemical  methods.  The 
author  there  concludes  that  the  yield  may  be  reduced  by  the  con- 
tinued selection  of  flat-round  tubers  which  are  rich  in  starch,  and 
increased  by  selection  of  cylindrical-long  tubers,  which  would  be 
poor  in  starch. 

Paulsen  (79)  makes  a  caustic  criticism  of  Fischer's  conclusions 
which  may  be  summed  up  as  follows :  The  form  whether  round  or 
long  is  characteristic  of  the  variety.  According  to  Fischer's  theory, 
a  seedling  plant  showing  round  tubers  should  be  rejected  immedi- 
ately because  they  are  less  capable  of  improvement.  Nevertheless, 
we  have  many  round  varieties  which  continue  to  give  exceedingly 
high  yields. 

In  1899  (40)  and  1900  (41),  Fruwirth  reports  that  selection  of 
timbers  from  high-yielding  plants,  as  well  as  the  choice  of  large 
tubers,  affects  the  yield,  and  recommends  the  selection  as  a  practical 
thing  especially  to  keep  up  the  vigor  of  the  variety.  In  1903  (42) 
the  same  author  reports  that  a  change  in  the  general  characteristics 
of  the  plants  of  a  variety  follows  only  gradually  when  the  variety 
is  brought  from  an  acclimated  place  to  one  with  a  different  soil  and 


408 


BULLETIN  No.  127. 


[August, 


climate.  He  argues  that  this  in  itself  is  a  proof  of  hereditary  trans- 
mission of  a  character  acquired  in  the  first  place.  Like  results  had 
been  obtained  already  by  Martinet  (70). 

Hess  (56)  concludes  that  selection  of  vigorous  mother  plants 
which  produce  many  tubers  will  bring  about  an  improvement  in 
the  yield.  His  data  do  not  warrant  a  definite  statement. 

Brumer  (14)  in  1891  came  to  the  same  conclusions,  but  he  ob- 
serves that  the  choosing  of  high-yielding  plants  only  increases  the 
yield  when  planted  on  a  fertile  soil.  When  planted  on  a  poor  soil, 
such  a  strain  will  set  many  tubers  but  they  will  be  small.  He  ob- 
serves further  that  the  use  of  vigorous,  healthy  plants  as  mother 
plants  gives  a  noticeable  protection  from  disease.  A  summary  of 
his  results  is  shown  in  the  following  table : 


Variety. 

Kind  of 
mother 
plant. 

Experiment  1. 

Experiment  2. 

Wt.  of 
seed 
tubers  g. 

Yield 
kilos. 

Diseased 
tubers 
percent. 

Wt.  of 
seed 
tubers  g. 

Yield 
kilos. 

Diseased 
tubers 
percent. 

Mag-rmm 
bonum  .  . 

large 
small 

45-50 
45-50 

96 

77 

none 
none 

40-45 
40-45 

92 
65 

2 
3 

Schnee- 
flocke  .  .  . 

large 
small 

35-40 
35-41 

55 
44 

6 
11 

35  40 
35-40 

61 

52 

8 
11 

In  1895  Sempolowski  (91  a)  reported  an  investigation  in  which 
he  selected  his  seed  potatoes  from  mother  plants  producing  at  least 
fifteen  tubers,  and  planted  them  in  comparison  with  such  ordinary 
stock  as  would  usually  be  planted.  His  yield  from  the  selected 
tubers  was  25285  Kg.  per  hectare  compared  with  24555  Kg.  per 
hectare  from  the  ordinary  seed. 

The  experiments  of  Liebscher  in  which  he  came  to  negative 
results  regarding  hereditary  transmission  of  tuber  variations  were 
continued  at  his  death  by  von  Seelhorst.  The  latter  concluded  in 
1897  that  their  experiments  up  to  that  time  contained  some  grave 
errors,  such  as  unequal  depths  of  planting,  non-uniformity  of  seed 
as  to  type  and  size,  etc.  These  errors  were  his  warrant  for  start- 
ing new  experiments  which  he  has  reported  in  three  notable  papers 
(89,  90,  91). 

The  experiments  were  with  four  varieties  and  I  give  below  the 
collected  results  for  the  last  year,  1903.  The  tubers  used  for  seed 
are  divided  into  two  classes,  large  and  small,  which,  as  can  be  seen 
does  away  to  a  large  extent  with  any  influence  due  to  differences  in 
weight  of  the  seed  used.  Determinations  of  starch  in  seed  tubers 
and  crop  were  also  made  and  there  was  a  notable  transmission  of 
starch  to  their  progeny  from  high  starch  tubers. 


I9o8.] 


IMPROVEMENT  OF  THE  POTATO. 


409 


Variety  and 
kind  of 
mother  plant. 

L/arge  seed  tubers. 

Small  seed  tubers. 

No. 

tubers 
used. 

Aver, 
wt.  g. 

Aver. 
wt.  of. 
crop  g. 

No. 

tubers, 
used. 

Aver, 
wt.  g. 

Aver, 
wt.  of 
crop  g. 

1.  Phobus 
large  yielding.  .  . 

33 

60.7 

478 

27 

34.4 

375 

small  yielding.  .  . 

15 

51.7 

301 

18 

30.1 

206 

2.  Frigga 
large  yielding  .  .  . 

32 

69.2 

319 

24 

32.5 

220 

small  yielding..  . 

12 

51.8 

113  3 

14 

27.7 

80.9 

3.  Viola 
large  yielding.  .  . 

25 

65.3 

372 

22 

36.6 

314 

small  yielding..  . 

23 

65.2 

282 

17 

30.8 

177 
494 

4.  Magnum  bonum 
large  yielding.  .  . 

38 

72.2 

631 

40 

38.2 

small  yielding.  .  . 

2 

87.0 

500 

10 

35.2 

603 

The  exception  in  the  case  of  Magnum  bonum  is  explained  by 
the  fact  that  the  seed  of  the  crop  from  this  variety  was  mixed  in 
1899  and  the  small  potatoes  used  here  may  have  been  from  large 
yielding  vines  before  that.  He  concludes :  "It  is  now  without 
question  to  me,  that  we  are  able  to  raise  the  yield  of  potatoes  by  a 
not  inconsiderable  degree  through  the  slight  care  in  selection  of 
seed,  and  also  to  prevent  to  a  very  great  degree  the  degeneration 
of  the  newly  improved  variety." 

Later  Martinet  (71),  Krzymowski  (62),  Eustace  (31)  and 
Parisot  (78)  have  experimented  along  this  line,  but  they  have  not 
generally  carried  on  their  investigations  long  enough  to  warrant 
definite  conclusions. 

Summing  up  all  evidence,  it  appears  that  there  are  variations 
which  may  be  transmitted  in  tuber  propagation,  but  that  in  prac- 
tice a  gain  is  rarely  made  by  their  selection.  In  general,  results 
have  been  obscured  by  seasonal,  climatic  and  local  soil  conditions 
which  have  a  tremendous  effect  and  which  are  not  constant  enough 
to  permit  tracing  marked  hereditary  transmission.  The  changes 
that  have  been  made  in  certain  cases  may  be  entirely  due  to  muta- 
tions and  not  fluctuations;  or  they  may  be  due  to  the  comparison 
of  tubers  that  were  physiologically  different,  such  as  diseased  and 
healthy,  or  immature  and  mature  tubers.  Proper  conclusions  can  be 
drawn  only  after  controlled  experiments  upon  an  accurately  meas- 
ured character  by  the  use  of  biometrical  methods. 


410  BULLETIN  No.  127.  [August, 

6.  HYPOTHESIS  OF  DEGENERATION 
ANALYSIS  OF  THK  QUESTION 

Very  closely  linked  with  the  possible  improvement  of  varieties 
by  the  selection  of  favorable  fluctuations,  and  its  equal  in  economic 
importance,  is  the  alleged  phenomenon  of  degeneration.  The  com- 
mon idea  is,  that  there  is  a  weakening,  "a  running  out"  of  a  variety, 
so  that  varieties  within  a  greater  or  less  number  of  years  are  cer- 
tain to  become  worthless  for  cultivation.  That  certain  varieties  in 
certain  localities  do  lessen  in  vigor  from  year  to  year  is  not  to  be 
disputed.  The  question  is  are  there  contributing  causes,  or  is  it  an 
inner  physiological  weakening,  a  protoplasmic  degeneration,  which 
must  take  place  owing  to  long  continued  bud  propagation.  The 
proper  analysis  of  the  question  is  of  great  importance;  for,  if  such 
a  degeneration  must  take  place  through  obedience  to  physiological 
laws,  our  good  varieties  are  necessarily  doomed  to  a  limited  life. 
A  proof  that  this  is  true,  would  make  a  great  difference  in  the 
practicability  of  methods  of  tuber  selection,  where  the  improvement 
—if  granted  possible — would  at  least  be.  slow.  Methods  of  selec- 
tion to  change  the  composition,  involving  expensive  analyses  of 
mother  tubers,  as  in  the  case  of  sugar  beets,  would  be  absolutely 
prohibited  unless  the  sexual  transmission  of  these  acquired  char- 
acteristics could  be  shown. 

The  common  method  of  reasoning  has  been:  Varieties  have 
diminished  in  yield  in  certain  places,  and  other  varieties  have  been 
obtained.  Nothing  more  is  heard  concerning  the  first  varieties; 
hence,  it  is  concluded  that  they  have  declined,  and,  figuratively 
speaking,  died. 

Hays  ( 52) x  indicates  the  general  belief  in  the  following  state- 
ment : 

"The  age  to  which  a  variety  propagated  by  annually  planting  the  root  cut- 
tings of  a  single  seminally  produced  plant  will  live  before  the  necessity  of 
renewal  by  sexual  reproduction  is  not  known.  But  since  standard  varieties  of 
potatoes  remain  prominent  for  only  about  a  third  of  a  century  there  is  some 
reason  for  the  belief  that  the  varieties  reach  their  period  of  old  age  or  senility 
in  that  time." 

The  period  of  prominence  of  varieties  is  hardly  a  measure  of  the 
question,  for  hundreds  of  men  are  annually  growing  seedlings  with 
which  they  hope  to  supplant  current  varieties  and  it  would  be  re- 
markable if  many  old  varieties  were  of  sufficient  merit  successfully 
to  hold  their  own.  But  nevertheless,  even  if  the  latter  statement 
were  not  true,  only  a  portion  of  the  question  is  settled,  Ehrenberg 


190$.]  IMPROVEMENT  OF  THE  POTATO.  411 

(29)  has  lately  discussed  the  question  in  all  of  its  bearings  from 
the  practical  standpoint,  and  divides  it  into  three  parts :  ( i )  the 
aging  (Altern)  or  senility  of  a  variety,  that  is,  a  degeneration  re- 
sulting from  inner  causes  because  of  a  prolonged  and  possibly  un- 
natural propagation  by  means  of  tubers;  (2)  the  deterioration 
(Ausarten)  caused  by  a  change  to  an  unfavorable  environment; 
(3)  the  loss  of  vigor  due  to  lack  of  selection  of  the  tubers  (Herab- 
ziichtung).  It  seems  that  the  last  two  might  be  united,  for,  set- 
ting aside  the  first  question,  it  must  be  variation  in  outside  influ- 
ences .that  causes  sufficient  variation  in  individual  plants  to  make  a 
basis  for  selection.  We  would  then  have  the  questions  of  variety 
senility,  and  of  incomplete  adaptation. 

The  latter  question  is  one  of  such  common  knowledge  that  it  is 
hardly  necessary  to  discuss  its  voluminous  literature.  It  should  be 
noted,  however,  that  this  has  nothing  to  do  with  the  question  of  the 
inheritance  of  partial  fluctuations. 

In  a  letter  written  by  Joseph  Cooper  (5),  of  New  Jersey,  in 
1799,  and  published  in  volume  one  of  the  Memoirs  of  the  Philadel- 
phia Society  for  promoting  Agriculture,  the  matter  seems  to  be  gen- 
erally recognized.  For  fifty  years,  Cooper  had  maintained  and 
improved  without  change,  strains  of  pumpkins,  early  peas  and  as- 
paragus. "He  made  similarly  successful  experiments  in  keeping 
and  improving  strains  of  the  potato  for  even  at  that  time  the  com- 
plaint was  'very  general,'  as  he  writes,  'that  potatoes  of  every  kind 
degenerate.' ' 

The  idea  has  changed  little  among  farmers  today,  although 
some  light  has  been  thrown  on  the  question.  In  1876,  Beal  (8) 
reported  an  experiment  in  which  a  variety  giving  good  yields  de- 
generated in  eight  years  so  as  to  produce  nothing,  although  other 
varieties  were  producing  good  crops  on  the  same  soil.  Fruwirth 
(42)  and  Martinet  (70)  have  explained  this  and  the  other  numer- 
ous experiments  of  the  same  nature  by  showing  that  there  is  a 
gradual  change  of  characters  that  takes  place  upon  changing  the 
locality,  either  for  better  or  worse  conditions.  In  other  words,  a 
variety  coming  from  a  locality  favorable  as  to  soil  and  climate 
to  one  unfavorable,  is  not  able  to  adapt  itself  rapidly  to  con- 
ditions, as  are  seed  propagated  plants  by  means  of  their  possibil- 
ities for  greater  numbers  of  combinations  of  characters.  There- 
fore there  is  a  final  disclosing  of  the  inadaptibility  of  the  variety, 
although  it  takes  place  more  or  less  slowly  owing  to  the  same  law. 

It  seems  to  the  writer  that  the  main  economic  question  still  un- 
solved is  whether  there  is  a  gradual  reduction  of  disease  resisting 


412  BULLETIN  No.  127.  [August, 

power  in  varieties.*  It  has  been  commonly  concluded  from  general 
observations  by  writers  on  potato  culture  that  such  is  the  case. 
There  are  varieties  which  in  comparative  tests  with  others,  give 
small  proportions  of  infected  plants  for  a  number  of  years  and  then 
show  a  notable  increase  in  this  proportion.  This,  however,  may  be 
easily  explained.  In  plants  propagated  by  seeds,  when  the  vigor  of 
any  particular  season's  produce  has  been  seriously  impaired,  the 
germinating  power  of  the  seed  is  likely  to  be  affected  and  they  are 
therefore  either  discarded  for  planting  or  fail  to  produce  plants  in 
the  field,  and  the  less  vigorous  strain  perishes.  With  potatoes,  an 
epidemic  of  any  particular  disease  scarcely  ever  completely  destroys 
the  crop.  The  tubers  weakened  in  vigor  are  planted  the  next  sea- 
son and  may  possibly  produce  plants  less  able  to  withstand  the  ef- 
fects of  futher  infection. 

We  have  already  seen  the  possibility  of  keeping  up  (not  im- 
proving) varieties  by  selection,  in  the  discussion  concerning  the 
transmission  of  tuber  variations.  Girard  (45),  who  had  probably 
a  wider  experience  than  any  other  investigator  in  the  subject, — 
working  as  he  did  for  eleven  years  with  sometimes  over  six  hun- 
dred co-operators, — sums  up  the  whole  matter  as  dependent  on 
seed  selection.  However,  the  strict  attention  he  paid  to  all  matters 
concerning  soil,  fertilizers,  planting  and  cultivation  shows  that  he 
really  laid  great  stress  on  favorable  environment.  He  says : 

"It  is  an  opinion  quite  broadly  held  that  varieties  of  potatoes  cultivated  con- 
tinually in  the  same  region,  are  certain  to  degenerate.  It  is  a  frequent  thing  to 
hear  large  potato  buyers  or  starch  manufacturers  declare  that  after  having  im- 
ported and  placed  at  the  disposal  of  their  growers  varieties  of  potatoes  noted  for 
their  large  crops,  they  have  seen  them  give  excellent  results  the  first  year,  fall 
away  the  second  year,  and  give  results  even  lower  than  the  native  potatoes  in 
the  third  year.  This  is  indeed  true  but  it  is  by  no  means  inexplicable ;  the  de- 
generation which  one  sees  in  this  circumstance,  does  not  result  from  a  natural 
weakening  of  the  variety;  it  simply  results  from  the  entire  lack  of  care  with 
which  the  plants  to  be  perpetuated  are  chosen.  All  the  good  tubers  are  sold  to 
the  market,  and  it  is  from  the  inferior,  discarded  tubers  that  has  been  demanded 
a  continuation  of  qualities  which  they  cannot  give.  I  have  demonstrated  prac- 
tically, and  have  established  the  fact  that  if  suitable  tubers  are  selected  for 
planting  and  the  cultivation  accomplished  with  the  needed  care,  the  quality  and 
quantity  of  the  crop  will  be  maintained  under  all  satisfactory  climatic  conditions." 

Since  such  degeneration  as  is  commonly  noticed  can  be  readily 
explained  without  resorting  to  any  hypothesis  of  "variety  senility," 
this  division  of  the  subject  is  still  to  be  discussed. 

*It  also  may  be  that  there  is  a  natural  selection  of  more  virile  strains  of  funei. 


1908.]  IMPROVEMENT  OF  THE  POTATO.  413 

BIOLOGICAL  EVIDENCE 

It  has  long  been  believed  by  a  number  of  investigators  that  a 
conjunction  of  paternal  and  maternal  nuclei  is  necessary  for  the 
"rejuvenescence  of  vigor"  in  the  species.  Life  has  been  considered 
to  be  a  cycle,  running  from  conjugation  to  conjugation  through  a 
greater  or  less  number  of  generations.  This  was  considered  by 
many  to  be  definitely  proved  when  Maupas  (72,  73)  showed  that 
colonies  of  Infusorians,  when  artifically  prevented  from  conjugat- 
ing, invariably  died  out  although  often  several  hundred  generations 
intervened.  Later  experiments  along  the  same  line  by  Calkins, 
however,  have  shown  that  a  change  in  diet  and  the  stimulus  of  a 
supply  of  chemical  salts  appear  to  be  all  that  is  necessary  for  con- 
tinued propagation  of  Infusorians  without  conjugation.  An  addi- 
tion of  an  extract  of  sheeps  brains,  was  all  that  was  necessary  to 
restore  his  colonies  to  full  vigor  after  the  62Oth  generation. 

The  classical  experiments  of  Tichomiroff  and  Loeb  have  shown 
that  artificial  parthenogenesis  may  be  induced  by  both  mechanical 
and  chemical  stimuli;  while  Boveri  and  Delage  have  developed 
even  non-nucleated  ovum  fragments  to  the  larval  stage.  As  one  re- 
sult of  these  facts,  we  must  conclude  that  fertilization  produces  two 
results :  a.  A  combination  of  hereditary  qualities ;  b.  A  physiolog- 
ical stimulus  to  growth.  But  since  other  stimuli  are  found  to  pro- 
duce cell  division,  it  is  hardly  reasonable  that  highly  specialized 
sexual  processes  should  have  been  developed  with  the  second  result 
as  their  primary  objects.  Indeed  Weismann  (105  v.  i  p.  343)  has 
concluded  that  the  sole  immediate  effect  of  conjugation  is  "the  com- 
bination of  the  hereditary  tendencies  of  two  individuals  into  one." 

It  appears  that  we  have  no  data  among  wild  plants  from  which 
we  are  compelled  to  conclude  that  continuous  bud  propagation  is 
opposed  to  any  natural  law.  Vines*  writing  of  the  Basidiomycetes 
says  "These  fungi  are  not  only  entirely  asexual  but  it  would  appear 
that  they  have  been  evolved  in  a  purely  asexual  manner  from  asex- 
ual ascomycetous  or  aecidiomycetous  ancestors.  The  basidiomycetes, 
in  fact,  afford  an  example  of  a  vast  family  of  plants  of  the  most 
varied  forms  and  habits,  including  hundreds  of  genera  and  species, 
in  which,  so  far  as  minute  and  long  continued  investigations  have 
shown,  there  is  not  and  probably  never  has  been,  any  trace  of  a  sex- 
ual process." 

Late  cytological  investigations  have  shown  sexual  processes,  or 
at  least  nuclear  fusions  similar  to  those  of  the  higher  plants  and 

*Vifles,  Nature  11:  p.  625,  quoted  by  Reid:    Principles  of  Heredity. 


414  BULLETIN  No.  127.  [August, 

animals,  in  some  of  these  fungi;  but  there  are  other  species,  and 
among  animals,  some  species  of  crustaceans,  which  reproduce  ex- 
clusively by  parthenogenesis.  Some  of  the  fungi  are  thought  to 
have  vestiges  of  degenerate  sexual  organs,  and  in  the  Crustaceans 
it  can  be  demonstrated  (105)  that  they  once  reproduced  sexually, 
by  their  possession  of  the  sac  which  once  served  for  receiving 
the  spermatozoa.  It  is  extremely  improbable  that  a  process  neces- 
sary or  even  advantageous  to  the  continuance  of  any  species  could 
have  been  allowed  to  degenerate  under  the  operation  of  natural  se- 
lection. 

In  higher  plants  we  have  numerous  examples  where  either  no 
seed  is  produced  or  where  seed  propagation  is  seldom  resorted  to 
and  yet  we  hear  no  serious  charges  of  degeneration.  Among  them 
may  be  given  the  banana,  hops,  strawberry,  sugar  cane  and  many 
of  the  grasses.  There  are  also1  certain  parthenogenetic  plants,  such 
as  the  dandelion,  that  are  certainly  in  no  danger  of  dying  out  from 
their  method  of  seed  production. 

The  fact  of  degeneration  in  potatoes  seems  to  have  been  ex- 
plained as  variety  senility  due  to  bud  propagation,  as  a  convenient 
prop  to  various  hypotheses  as  to  the  function  of  sex;  and  this  con- 
clusion on  theoretical  grounds  is  decidedly  unproved. 

EXPERIMENTAL  EVIDENCE 

So  far  as  I  am  able  to  learn  the  senility  theory  was  first  pro- 
pounded about  1806  by  Knight  (61)  although  he  did  not  lay  special 
stress  on  potatoes.  His  hypothesis  was  that  all  varieties  propagated 
by  buds  (particularly  fruits)  have  a  most  productive  period  when 
they  are  of  middle  age  and  then  become  "subject  at  no  very  distant 
period  to  the  debilities  and  diseases  of  old  age." 

Aitken  (i)  first  applied  the  hypothesis  to  potatoes  in  1837. 
He  believed  that  although  most  fruits  were  produced  from  seed 
each  year,  a  potato  variety  was  a  single  plant  propagated  yearly 
through  its  tubers,  and  must  grow  old  in  the  process.  The  first 
sign  of  this  weakening  of  the  variety,  he  says,  is  a  lack  of  blossoms. 

In  Germany,  Berchtold  (9)  in  1842  accepted  Aitken's  view  with 
limitations.  He  considered  that  disease,  climate,  soil,  cultivation 
and  other  conditions  were  the  important  factors  to  be  considered. 

Later  Heine  (53)  of  Emersleben,  who  was  for  ten  years  the 
chief  German  writer  on  potatoes,  was  very  pronounced  in  his  ac- 
ceptance of  Aitken's  theory,  and  was  followed  by  many  of  his 
countrymen.  He  speaks  continually  of  "the  unalterable  law  of  na- 
ture that  only  through  sexual  seed  propagation  is  it  possible  to 


IMPROVEMENT  OF  THE  POTATO.  4l^ 

keep  potato  varieties  lastingly  high  in  yield."  It  is  exceedingly  in- 
teresting to  note,  however,  that  Westermaeier  (106)  who  suc- 
ceeded Heine  in  his  work  has  finally  come  to  the  conclusions  that 
in  Heine's  results  the  contributing  factors  were  not  differentiated 
from  the  real  question,  and  that  it  seems  to  him  that  it  is  question- 
able whether  there  is  any  such  thing  as  variety  senility. 

The  later  conformers  to  Heine's  views  are  Paulsen  (43),  Cim- 
bal  and  Marek. 

The  first  weighty  objection  to  this  theory  was  made  by  Julius 
Kiihn  (64)  in  1871.  He  says:  "The  theory  of  a  degeneration  of 
the  potato  is  disproved  as  untenable"  and  continued  for  several 
years  thereafter  to  combat  Aitken's  theory.  Busch  (15)  continued 
the  opposition  and  seems  to  be  really  the  first  to  recognize  the  true 
question.  He  says :  "A  degeneration  in  the  sense  of  an  increasing 
deterioration  through  the  weakness  of  old  age,,  does  not  exist." 
His  views  were  endorsed  and  enlarged  upon  by  Wollny  (108), 
Liebscher  (66),  Girard  (45),  Thiele  (96)  and  Fischer  (33)  who 
have  all  considered  the  question  apart  from  that  of  degeneration 
through  lack  of  adaptation  to  environment. 

Ehrenberg  (29)  in  1904  makes  a  complete  survey  of  data  of 
Heine,  of  the  deutschen  Kartoffelkultursta'tion,  and  of  Paulsen,  the 
first  and  last  of  these  running  from  1877  to  1903.  He  discusses  all 
the  contributing  sources  of  error  and  comes  to  the  conclusion  that 
"Kin  Altern  der  Kartoffel  gibt  as  aller  Wahrscheinlichkeit  nicht." 
And  indeed,  it  appears  that  the  people  who  have  considered  this 
single  question  are  unanimous  in  opposition  to  the  hypothesis  of 
variety  senility.  The  English  and  American  writers  do  not  seem 
to  have  considered  the  questions  apart,  although  Bailey  (5  p.  380) 
and  probably  others  have  recognized  the  division.  He  says : 

"The  presumption  is  that  varieties  propagated  by  buds  wear  out  sooner 
than  those  propagated  by  seeds,  for  the  experiments  of  Darwin  and  others  have 
shown  that  the  special  office  of  seed  propagation  is  to  increase  the  virility  of  the 
species  through  cross  fertilization.  It  must  follow  therefore,  that  in  the  ab- 
sence of  cross  fertilization  virility  must  be  less. 

"But  we  do  not  need  to  consider  this  phase  of  the  question,  for  we  are 
concerned  with  variation  (that  is,  running  out)  rather  than  with  ultimate 
longevity  (or  wearing  out).  Further,  it  is  also  probable  that  any  tendency 
toward  weakness  through  lack  of  fertilization  is  fully  counterbalanced  by  the 
protection  which  such  varieties  receive  under  cultivation." 

The  work  of  the  U.  S.  Agricultural  Experiment  Stations  bear- 
ing the  nearest  relation  to  this  question  are  those  experiments  deal- 
ing with  cormparative  value  of  home  grown  and  northern  seed 
tubers.  There  is  a  wide  spread  belief  both  in  this  country  and  in 


416  BULLETIN  No.  127.  [August, 

England  that  northern  grown  seed  is  the  superior,  and  should  be 
obtained  every  two  years  or  so  because  of  degeneration.  It  is 
interesting  to  note  that  in  experiments  at  six  stations*  in  the  early 
nineties,  all  show  results  slightly  in  favor  of  home  grown  varieties. 
It  is  probable  that  in  these  experiments  more  care  was  paid  to  seed, 
fertilizers  and  cultivation  than  is  usual  to  growers,  resulting  well 
for  home  grown  seed ;  nevertheless,  had  the  results  been  different,  it 
would  only  have  shown,  either  that 'the  northern  grown  were  better 
adapted  to  such  climate  or  the  soils  there  found,  or  that  in  coming 
from  growers  who  made  a  commercial  business  of  supplying  seed 
tubers,  they  had  been  given  better  care  in  regard  to  selection  and 
environmental  conditions. 

Relying  for  our  conclusions  on  the  philosophical  grounds  and 
the  practical  work  of  the  German  and  French  investigators,  it  seems 
tenable  that  there  is  no  variety  senility  and  that  we  are  warranted 
in  excluding  this  from  our  calculations  as  to  commercial  methods 
of  producing  varieties  adapted  to  certain  conditions.  The  more 
serious  practical  question,  is  the  manner  in  which  outside  pernicious 
influences  are  to  be  avoided.  As  methods  of  cultivation  and  seed 
selection  are  pretty  well  established  and  soil,  plant  food  and  climatic 
conditions  can  be  determined  and  partially  controlled  in  each  local- 
ity, it  seems  to  the  writer  that  here  again  the  matter  of  disease  con- 
trol is  the  thing  of  primary  importance.  It  is  questionable,  with- 
out disease  resistance  or  comparatively  certain  disease  control,  if 
expensive  work  should  be  done  to  improve  varieties  in  particular 
characters  such  as  starch  content,  by  selection  of  seedlings  on  the 
basis  of  a  chemical  analysis.  For  it  is  reasonably  certain  that  we 
could  not  expect  this  improvement  to  be  transmitted,  if  we  were 
forced  by  loss  of  vigor  due  to  disease  attacks  to  return  to  sexual 
propagation.  The  latter,  however,  is  a  matter  which  we  can  say  is 
yet  unproved. 


^Illinois,  Vermont,  Maryland,  Georgia,  Louisiana,  and  Missouri. 


ioo#.]  IMPROVEMENT  OF  THE  POTATO.  417 

7.  DISCONTINUOUS  VARIATIONS 
MUTATIONS 

It  has  long  been  recognized  that  in  potato  varieties  there  some- 
times appear  marked  bud  variations  which  when  propagated  are 
true  to  type.  If  we  accept  DeVries'  idea  of  mutations,  and  if  we 
believe  that  bud  mutations  are  of  practically  the  same  nature  as  seed 
mutation ;  then  they  may  be  either  progressive,  degressive  or  retro- 
gressive. Such  variations  which  have  been  noticed  have  always 
been  relatively  wide  ones,  but  it  is  not  inconsistent  with  the  theory 
to  have  mutations  which  are  within  the  limit  of  fluctuating  varia- 
tions. As  the  writer  understands  the  question,  these  mutations  may 
be  either  bud-mutations,  which  may  not  be  propagated  by  seed ;  or 
mutations  affecting  the  gametic  structure,  which  will  always  be  in- 
herited unless  new  mutations  intervene. 

Darwin  (21)  mentions  three  cases,  one  in  which  a  single  white 
eye  in  the  purple  variety  Forty  fold,  became  the  "parent"  of  a  white 
variety.  In  another  case  this  same  variety  produced  a  whole  white 
tuber  which  bred  true.  The  third  case  was  that  of -the  white  Kemp 
potato  which  produced  a  red  spot  which  was  propagated  and 
yielded  a  variety  of  much  prominence,  which  was  called  Taylor's 
Forty-fold.  In  the  United  States  there  has  been  a  number  of  vari- 
eties on  the  market  for  several  years  which  have  originated  in  this 
way.  Among  them  are  Thorburn's  Late  Rose,  the  White  Victor  and 
White  Early  Ohio.  I  should  roughly  estimate  that  less  than  0.5 
percent  of  our  present  varieties  are  from  bud-mutation.  The  gen- 
eral belief  is  that  these  variations  are  confined  to  tuber  color  or  pos- 
sibly to  tuber  color  and  shape.  Wohltmann  (43)  has  offered  an  ex- 
ception; a  variation  in  flower  color  in  the  Leo  variety  although  it 
was  unknown  whether  the  variety  came  from  one  or  several  seed- 
lings. It  certainly  seems  that  the  variations  are  almost  always  con- 
fined to  the  tubers,  but  this  should  be  expected  as  the  tubers  are  the 
modified  part.  The  probability  is  that  color  is  the  only  character 
that  is  easily  gauged,  and  that  if  accurate  metnuus  of  estimating 
other  characters  were  used,  they  too  would  be  found  to  vary.  The 
supposed  rarity  of  these  occurrences  has  made  them  of  little  com- 
mercial importance,  but  it  is  very  possible  that  with  strict  search, 
they  might  be  shown  to  occur  much  oftener  than  is  expected. 

As  stated  before,  data  which  I  have  collected  appear  to  show 
that  bud-mutations  are  usually — and  possibly  always — the  loss  of 
the  dominant  character  of  an  allelomorphic  pair,  with  the  conse- 
quent appearance  of  the  recessive  character.  This  data  will  be  pub- 
lished in  a  separate  paper. 


418  BULLETIN  No.  127.  [August, 

8.  GRAFT-HYBRIDS 

We  have  in  graft-hybrids  another  method  in  which  there  may  be 
a  possibility  of  an  improvement  of  the  potato. 

There  is  still  a  great  deal  of  argument  as  to  the  authenticity  of 
graft-hybrids  which  have  been  reported.  The  negative  reasoning 
being  chiefly  theoretical,  owing  to  their  present  inexplicability. 

Darwin  (21)  collected  a  large  number  of  cases  where  asexual 
hybrids  of  the  potato  seem  to  have  been  made.  He  himself  was 
fully  convinced  as  to  their  authenticity  although  he  recognized  the 
fact  that  the  scoffer  might  attribute  them  to  bud  variation  induced 
by  the  graft.  He  argues  that  the  variation  was  always  between  the 
parent  forms. 

Daniel  (19,  20)  who  has  made  by  far  the  most  extended  study 
of  grafts,  says  that,  "While  formerly  it  was  considered  that  grafted 
scions  lost  none  of  their  own  characteristics  and  acquired  no  new 
ones  from  the  stocks  on  which  they  were  grafted,  recent  work 
indicates  that  this  view  must  be  modified."  He  states  that  hybrid- 
grafts  can  be  fixed  and  propagated ;  and  mentions  the  Edouard  Le- 
fort  potato  produced  by  vine  graft  of  Majolin  and  Imperator  and 
partaking  of  the  character  of  each.  He  believes,  however,  that 
asexual  hybridization  is  neither  constant,  regular  nor  very  frequent. 

Biffen  (n)  grafted  tubers  with  different  characters,  and  while 
convinced  of  the  authenticity  of  the  phenomenon,  he  states  that 
"Tubers  in  which  two  types  are  blended,  never  occur."  In  halving 
the  tubers  transverely,  each  portion  was  indistinguishable  from  one 
of  its  parents.  Each  half  of  the  tuber  showed  all  the  characters  of 
one  parent  and  not  certain  dominant  ones.  The  graft-hybrid  was  in 
this  respect  different  from  the  seed  hybrid. 

There  is  at  present  no  cytological  explanation  of  such  a  phe- 
nomenon, but  from  the  apparent  ease  with  which  hybrid-grafts  are 
made,  or  at  least  by  which  bud  variations  are  caused  through  such 
stimulus,  this  seems  to  be  a  very  interesting  field  for  investigation. 
If  in  potato  improvement  we  could  in  time  learn  to  make  a  reason- 
able percentage  of  successful  hybrids  and  the  characters  would  blend, 
it  might  settle  the  quandary  in  which  we  are  at  present,  in  trying  to 
get  crosses  with  many  of  the  excellent  varieties  which  produce  little 
or  no  viable  pollen.  On  the  other  hand,  if  it  finally  proves  that 
there  is  not  a  true  hybrid  formed,  this  method  may  still  prove  valu- 
able as  a  means  of  obtaining  bud-mutations. 


1908.]  IMPROVEMENT  OF  THE  POTATO.  419 

9.  QUALITY 
HISTORICAL 

In  1897  Coudon  and  Boussard  (18)  came  to  the  conclusion  on 
the  ground  of  their  tests  with  thirty-four  varieties  of  potatoes  that 
their  culinary  value  is  dependent  upon  the  chemical  composition, 
and  that  it  varies  directly  as  the  nitrogen  content  and  inversely 
as  the  starch  content,  that  is  culinary  value  =  "^1"*!"-  Potatoes 
with  a  high  starch  content  were  disintegrated  by  boiling,  and  pota- 
toes with  a  high  nitrogen  content  resistant. 

Their  analyses  were  made  of  four  physical  divisions  of  the  po- 
tato as  shown  in  figures.  These  parts  they  designated,  from  out- 
side to  inside,  as  skin,  cortical  layer,  outer  medullary  layer  and  in- 
ner medullary. 


FIG.  5.     ZONES  OF  THE  POTATO.     (AFTER  COUDON  AND  BOUSSARD.) 

a.  Cortical  layer. 

b.  External  medullary  layer. 

c.  Internal  medullary  layer. 

The  outer  skin  is  the  colored  portion  and  may  be  completely 
separated  from  the  part  underneath.  The  cortical  or  fibre-vascular 
layer  lies  next  and  is  easily  distinguished  by  the  separating  line  of 
vascular  bundles.  In  the  interior  the  inner  medullary  layer  appears 


420 


BULLETIN  No.  127. 


[August, 


like  an  undeveloped  stem  branching  out  toward  the  eyes.  The  re- 
sults of  their  analyses  of  these  parts,  calculated  to  the  fresh  basis 
are: 

COMPOSITION  OF  THE  DIFFERENT  ZONES  OF  THE  POTATO  TUBER 


Variety. 

Zone. 

Water. 

Starch. 

Total 
nitrogenous 
matter.* 

Cortical  

72  74 

21.14 

1  91 

Bleue 
geante. 

Out.  med  
In.  med  

74.33 
81  72 

19.78 
12.30 

1.88 
2.14 

72.92 

22.45 

1.84 

Czarine. 

78.87 

15.64 

2.17 

In.  med  

84  48 

10.50 

2.17 

Saucisse. 

Cortical-f 
Epidermis  
Out.  med  

78.72 
79  12 

14.38 
13  47 

2.22 
2.39 

In.  med.  .  .  . 

80  73 

12.31 

2.62 

The  water  and  nitrogen  contents  increase  as  we  go  from  the 
outer  to  the  inner  zones,  while  the  starch  content  decreases.  It  is 
also  interesting  that  the  percent  of  proteid  nitrogen  to  the  total  ni- 
trogen decreases  in  the  inner  zones;  the  former  being  68.7  percent 
in  the  cortical  layer,  56.0  percent  in  the  outer  medullary  layer  and 
47.3  percent  in  the  inner  medullary  layer. 

This  work  was  believed  to  give  a  chemical  basis  for  the  selection 
for  planting,  of  tubers  which  were  of  better  table  quality.  It  should 
be  noted,  however,  that  the  standard  for  table  quality  in  France  is 
decidedly  different  from  that  in  the  United  States.  The  accepted 
method  of  cooking  there  is  frying  in  deep  fat,  for  which  a  potato 
which  holds  its  form  is  desired ;  while  in  this  country  probably  nine- 
tenths  of  the  consumption  is  of  boiled  potatoes,  which  are  desired 
dry  and  mealy.  Potatoes  imported  from  Vilmorin,  which  I  have 
examiner! ,  r>^r1v  all  possessed  a  yellow  flesh,  a  strong  flavor,  and 
were  firm  and  soggy  after  boiling. 

Shortly  after  the  appearance  of  this  work,  Frisby  and  Bryant 
(38)  reported  separations  and  analyses  of  these  different  zones  in 
the  American  variety  "White  Star,"  without  separating  the  outer 
and  inner  medullary  layers,  and  found  the  following  composition : 

Zone  Water  percent       Proteid  N.          Total  N.       N.  free  extract 

Cortical  layer   83.2  .24  .36  12.6 

Outer  and  inner  Med 81.1  .18  .32  15.7 

*Probably  total  Nx6.25  although  it  is  not  stated. 


1908.] 


IMPROVEMENT  OF  THE  POTATO. 


421 


These  results  are  in  direct  opposition  to  Condon's  and  Bous- 
sard's  as  to  nitrogen  and  starch  but  the  discrepancy  may  have  been 
due  to  the  different  methods  of  determination.  Nitrogen  free  ex- 
tract gives  total  carbohydrates  minus  crude  fibre,  at  all  times,  while 
a  direct  starch  determination  is  very  different  when  made  in  the 
fall  from  one  made  in  the  spring  when  large  quantities  of  starch 
have  been  changed  to  sugar. 

In  1901  Waterstradt  and  Willner  (104)  reported  extended 
investigations  on  the  same  subject.  Their  results  are  more  appli- 
cable to  American  conditions  for  the  reason  of  similarity  of  stand- 
ard of  quality  in  Germany  and  America.  Nine  varieties  were  used, 
each  of  which  was  grown  on  two  separate  fields.  Of  these  varie- 
ties, three  were  recognized  to  be  of  good  table  quality,  three  were 
coarse  starch  producing  varieties  and  three  were  on  the  border  line 
between  the  two.  I  give  here  the  average  composition  only  of  the 
first  and  second  classes : 


Place 
grown. 

Class. 

Zone. 

Fresh  basis. 

Dry  basis. 

Dry 

Tot.  N. 

Starch. 

Dry 

Tot.  N. 

Starch. 

mat. 

mat. 

Eating 

Cor  .... 

24.3 

0.336 

18.17 

100. 

1.34 

75.03 

var. 

Med..  . 

19.8 

0.363 

14.74 

100. 

1  85 

74.50 

Berlin 

Exp. 

Field. 

Coarse 
starch 

Cor  .... 
Med.  .. 

26.9 
23.1 

0.359 
0.355 

20.61 
17.76 

100. 
100. 

1  34 

1  55 

75.68 
76.87 

var. 

Eating- 

Cor  

27.3 

0.365 

100. 

1.35 

var. 

Med.    . 

24.1 

0.391 

100 

1  56 

Marien 

Field. 

Coarse 
starch 

Cor  

Med.  .. 

30.6 

27.3 

0.354 
0.383 

100. 
100. 

1.17 
1.42 



var. 

This  table  shows  that  potatoes  of  better  table  quality  are 
markedly  lower  in  starch  than  the  others,  as  was  to  be  expected 
from  the  German  classification.  The  dry  matter  in  the  cortical 
layer  is  regularly  higher  than  in  the  medullary  layers,  as  is  the 
starch  content  when  calculated  to  the  fresh  basis.  When  calculated 
to  the  water  free  basis,  however,  the  starch  variations  are  slight. 
The  total  nitrogen  variations  corroborated  the  results  of  Coudon 
and  Boussard. 


422 


BULLETIN  No.  127. 


[August, 


In  order  to  find  the  proportion  of  cortical  layer  and  inner  medul- 
lary layers,  the  authors  cut  the  potatoes  in  half  through  the  long 
diameter,  marked  the  line  of  demarcation  of  the  two  layers  on 
paper  and  weighed  the  corresponding  slips.*  The  average  of  all  of 
the  good  eating  varieties  in  proportion  of  cortical  layer  to  inner 
medullary  layers  was  100:121.5,  while  the  proportion  in  the  coarse 
varieties  was  100:140.4.  The  actual  cooking  tests  bore  out  their 
opinion  of  the  relative  cooking  value  of  the  varieties  as  expressed 
in  their  classification,  and  they  concluded  that  chemical  composition 
could  not  be  used  as  a  basis  of  selection  for  cooking  value. 

In  1905  Gilmore  (44)  published  an  excellent  paper  in  which  he 
tentatively  concluded  that  the  culinary  value  of  the  potato  depended 
not  so  much  upon  its  chemical  composition  as  upon  its  anatomical 
and  perhaps  its  physiological  structure. 

EXPERIMENTAL 
COMPOSITION  OF  DIFFERENT  PARTS 

The  first  object  in  this  work  was  to  see  if  American  varieties 
and  especially  if  within  a  variety,  the  table  quality  is  dependent 
upon  the  total  nitrogen  content. 

The  two  varieties  Rural  New  Yorker  No.  2  and  Carman  No.  3 
were  selected  as  being  representative  popular  varieties.  Careful 
mechanical  separations  of  the  different  zones  were  made  in  five  in- 
dividual potatoes  of  each  variety,  after  the  manner  of  Condon  and 
Boussard.  Dry  matter  was  determined  at  104  degrees  C  in  a  cur- 
rent of  hydrogen,  and  total  nitrogen  was  determined  by  the  regular 
Kjeldahl  method,  as  were  all  similar  determinations  here  reported. 
The  averages  of  the  results  of  each  variety  are  shown  in  the  fol- 
lowing table : 

TABLE  3.     COMPOSITION  OF  PARTS  OF  THE  POTATO 


Variety. 

Zone. 

Dry  matter, 
percent. 

Tot.  N. 
fr.  bas., 
percent. 

Tot.  N. 
dry  bas., 
percent. 

Rural 

Cortical  

20  95 

0.46 

2.20 

N.  Y. 

No.  2. 

Outer  med  .... 
Inner  med  

18.46 
14.04 

0.47 
0.45 

2.56 
3.23 

Cortical  

22  20 

0.49 

2.23 

Carman 
No.  3. 

Outer  med.  .  .  . 
Inner  med  .... 

19.41 
14.92 

0.51 
0.52 

2.63 
3.49 

*This  method  does  not  show  the  correct  relation.     If  the  potatoes  were  considered  as  sper- 
ical,  the  relation  would  be  (whole  dia meter) 3-(medullary  diameter)3:   (medullary  diameter3). 


IMPROVEMENT  OF  THE  POTATO. 


423 


The  content  of  dry  matter  is  quite  variable  and  regularly  de- 
creases from  the  outside  to  the  inside  of  the  three  zones.  The 
total  nitrogen  content  is  only  slightly  variable  in  the  three  zones, 
though  showing  a  regular  increase  to  the  inner  medullary  layer, 
when  calculated  to  the  dry  basis,  owing  to  the  variability  of  the 
water  content.  Ash  determinations  made  on  ten  samples  varied  little 
from  0.90  percent  on  the  fresh  basis,  showing  that  carbohydrates, 
estimated  by  difference,  are  higher  in  the  cortical  layer,  and  quite 
low  in  the  inner  medullary  layer.  From  this  we  may  conclude  that 
there  is  a  difference  in  time  of  cooking  in  the  different  zones  of  the 
potato,  and  that  the  glistening  appearance  of  the  cortical  layer  after 
boiling  would  be  accounted  for  by  its  larger  starch  content  breaking 
open  the  cell  walls. 

SAMPLING 

Since  there  is  such  a  difference  in  the  composition  of  these  dif- 
ferent zones,  it  is  extremely  difficult  to  obtain  a  correct  sample  of 
the  tubers  for  analyses  without  spoiling  them  for  cooking  tests  or 
for  planting.  A  number  of  methods  were  tried,  the  one  giving  the 
most  satisfactory  results  being  that  of  a  cylinder  cut  with  a  twelve 
mm.  cork  borer,  parallel  to  the  long  diameter,  but  a  little  to  the 
side.  This  takes  in  only  a  portion  of  the  inner  medullary  layer  and 
compares  well  with  the  composition  of  the  whole  potato.  The 
greatest  difference  in  five  determinations  of  total  nitrogen  on  indi- 
vidual tubers  was  0.04  percent  calculated  to  the  fresh  basis. 

TABLE  4.    VARIATIONS  IN  SAMPUNG 


Potato  No. 

Total  N.  per  cent 
in  cylinder. 

Total  N. 
in  whole  tubers. 

1 
2 
3 
4 
5 

0.37 
0.43 
0.49 
0.42 
0.46 

0.34 
0.41 
0.50 
0.43 
0.44 

This  method  has  been  used  in  all  subsequent  determinations 
when  tubers  were  to  be  used  for  cooking  tests  for  planting. 

RELATIONS  OF  TOTAL  NITROGEN  CONTENT  AND  QUALITY 

To  ascertain  the  relation  of  total  nitrogen  content  to  quality,  a 
number  of  tubers  of  the  Rural  New  Yorker  No.  2  variety  in  which 


424 


BULLETIN  No.  127. 


[August, 


total  nitrogen  and  dry  matter  had  been  determined,  were  tested  by 
boiling.  Corks  were  tied  in  the  holes,  whence  the  sample  for  analy- 
sis had  been  taken.  City  water  from  artesian  wells,  containing  a 
considerable  amount  of  salts,  was  used,  but  no  sodium  chlorid  was 
added.  On  account  of  the  amount  of  work  necessary  to  secure 
samples  with  a  sufficient  variation  in  nitrogen  content,  only  ten  of 
each  kind  were  used.  So  small  a  number  makes  the  probable  error 
large,  especially  as  no  method  of  judging  the  quality  has  been  de- 
vised except  an  arbitrary  personal  judgment.  The  flavor  and  the 
table  quality  aside  from  flavor  were  judged,  dividing  the  array  into 
five  different  classes.* 

Their  selection  for  high  nitrogen  content  did  not  seem  to  affect 
the  average  of  the  two  classes  in  weight  or  dry  matter  to  any  consid- 
erable extent,  as  is  shown  below : 

TABLE  5.    QUALITY  OF  HIGH  NITROGEN  POTATOES 
AVERAGES:    WT.  2o6g.    PERCENT  DRY  MATTER 21.09.    PERCENT  N.  DRY  BASIS  2.27 


Potatoes 
used. 

Average 
total  N. 
content. 

Quality  and  appearance. 

Flavor. 

good. 

fair. 

med. 

poor. 

very  p. 

good. 

fair. 

med. 

poor. 

very  p. 

10 

0.48 

1 

5 

2 

1 

1 

0 

3 

5 

2 

0 

TABLE  6.     QUALITY  OF  Low  NITROGEN  POTATOES 
AVERAGES  :    WT.  2i8g.    PERCENT  DRY  MATTER  21.99.    PERCENT  N.  DRY  BASIS  1.62 


Potatoes 
used. 

Average 
total  N. 
content. 

Quality  and  appearance. 

Flavor 

good. 

fair. 

med. 

poor. 

very  p. 

good. 

fair. 

med. 

poor. 

very  p. 

10 

0.36 

1 

4 

2 

2 

1 

1 

3 

4 

2 

0 

The  tables  indicate  that  variation  in  nitrogen  content  does  not 
have  a  noticeable  effect  on  quality,  although  there  is  a  slight  indi- 
cation that  extremely  high  nitrogen  might  make  the  flavor  more 
pronounced.  High  nitrogen  potatoes  can  therefore  be  propagated 
without  correlation  adverse  to  quality,  weight  or  dry  matter. 

*It  should  be  noticed  that  in  these  tests  by  arbitrary  standard  only  the  results  of  any  one 
experiment  should  be  compared  with  each  other,  for  it  is  impossible  to  keep  in  mind  an  arbi- 
trary standard  from  week  to  week  to  compare  separate  tests.  The  tubers  in  every  case  were 
known  by  numbers  only. 


1908.] 


IMPROVEMENT  OF  THE  POTATO. 


425 


RELATIONS  OF  DRY  MATTER  AND  QUALITY 

In  the  same  manner  as  above,  selections  of  potatoes  of  different 
dry  matter  content  were  tested.  As  far  as  was  possible  tubers  of 
relatively  the  same  weight  were  used,  in  order  to  have  the  same  time 
of  cooking.  Otherwise  the  selection  was  entirely  by  dry  matter: 

TABLE  7.     QUALITY  AS  RELATED  TO  DRY  MATTER 


Potatoes 
used. 

Dry 

matter. 

Average 
total  N. 
fresh  b. 

Average 
wt. 

Quality  other  than 
flavor. 

Flavor. 

£• 

f. 

m. 

P- 

v.  p. 

8- 

f. 

m. 

P- 

v.  p. 

16-17% 

8 

Aver. 

0.40 

219 

0 

0 

1 

3 

4 

0 

0 

0 

2 

6 

--  ,  ...". 

16.50 

17-18% 

10 

Aver. 

0.42 

232 

0 

2 

3 

3 

2 

0 

0 

1 

6 

3 

17.56 

19-20% 

10 

Aver. 

0.45 

228 

2 

4 

4 

0 

0 

1 

3 

4 

2 

0 

•'     '    '  ,' 

19.62 

21-22% 

10 

Aver. 

0.44 

204 

1 

4 

3 

2 

0 

1 

5 

4 

0 

0 

21.65 

23-24% 

10 

Aver. 

0.44 

220 

2 

4 

4 

0 

0 

1 

4 

5 

0 

0 

23.44 

25-28% 

8 

Aver. 

0.38 

208 

1 

3 

3 

1 

0 

2 

3 

3 

0 

0 

26.09 

This  table  shows  that  there  is  a  lower  limit  in  amount  of  dry 
matter  or  more  probably  of  carbohydrates,  below  which  tubers  can- 
not be  of  good  quality.  In  this  variety  it  is  about  18  percent  dry 
matter  or  probably  about  15  percent  starch. 

When  the  dry  matter  is  above  this  lower  limit,  the  quality  does 
not  seem  to  be  directly  affected.  It  may  be  that  this  lower  limit  is 
different  in  different  varieties,  and  that  owing  to  the  general  low 
dry  matter  of  these  samples  the  standard  of  quality  was  put  too  low. 
However  some  excellent  potatoes  were  found  with  a  total  dry  mat- 
ter as  low  as  19  percent. 

Waterstradt  and  Willner  showed  that  in  certain  German  varie- 
ties those  tubers  with  very  high  starch  content  were  of  coarse  qual- 


426 


BULLETIN   NO. 


[August. 


ity.  We  found  no  potatoes  nearly  up  to  this  limit,  but  from  general 
experience  we  should  conclude  that  potatoes  with  a  starch  content 
above  a  certain  limit  would  easily  fall  to  pieces,  or  if  the  cell  walls 
were  strong  enough  to  hold  together  under  such  pressure,  they  must 
necessarily  be  coarse  and  woody. 

PHYSICAL  STRUCTURE  AND  QUALITY 

The  writer  was  led  first  by  Coudon's  and  Boussard's  work  to 
believe  that  the  physical  structure  held  some  relation  to  the  table 
quality.  Microscopical  examination  of  the  structure  of  the  potato 
bears  out  the  chemical  analyses  of  the  different  zones. 


FIG.   6.     a.  OUTER  SECTION  OF  CORTICAL  LAYER,     b.  INNER  SECTION   OF  CORTICAL. 

LAYER. 

(Figures  6  and  7  from  the  same  tuber.) 

The  corticaL  layer  (figure  6),  below  the  first  few  layers  of 
cells  which  are  removed  with  the  skin,  shows  a  remarkably  larger 
amount  of  starch  in  the  cells,  than  does  the  internal  medullary  layer 
(figure  7).  The  starch  content  of  the  external  medullary  layer  is 
also  greater  than  that  of  the  internal.  The  grains  of  starch  in  the 
cortical  and  external  medullary  layers  besides  existing  in  greater 
numbers  per  cell,  are  generally  of  larger  average  size.  The  paucity 
of  starch  in  the  internal  medullary  layer  causes  the  cells  to  be  only 
partially  filled  with  the  cooked  starch  and  the  cell  walls  are  scarcely 
ever  ruptured.  In  the  cortical  layer,  on  the  other  hand,  the  amount 
of  starch  is  such  that  in  the  swelling  due  to  cooking,  the  cells 
are  filled  completely  and  many  of  them  ruptured,  causing  the  mealy 
appearance  so  much  desired  by  tfae  consumer. 


IMPROVEMENT  OF  THE  POTATO 


FIG.  7.    a.  SECTION  NEAR  THE  VASCULAR  BUNDLES  SHOWING  PORTION  OF  EXTERNAL 

MEDULLARY  LAYER,      b.   SECTION  OF  INTERAL   MEDULLARY  LAYER. 

It  is  quite  evident  then  that  potatoes  having  as  far  as  possible 
a  homogeneous  flesh  and  containing  as  large  an  amount  as  possible 
of  cortical  and  outer  medullary  layers  in  proportion  to  inner  medul- 
lary layer,  should  be  of  the  finest  quality.  f 

This  has  been  shown  to  be  a  fact  in  experiments  with  fifteen 
American  varieties  even  though  cooked  after  having  been  split*  in 
half,  which  is  manifestly  a  disadvantage. 


FIG.  8.  CROSS  SECTIONS  OF  POTATO  CF  GOOD  QUALITY.  LARGE  CORTICAL  AND  EXTER- 
NAL MEDULLARY  LAYERS,  AND  SMALL  OR  FINELY  DIVIDED  INTERNAL  MEDULLARY 
LAYER. 


*In  a  number  of  these  tests  the  halv«s  of  the  potatoes  were  fastened  together  again  before 
cooking,  in  order  to  make  the  test  as  near  as  possible  like  ordinary  practice.  The  judgment 
of  the  quality  was  made  by  two  different  persons.  The  tubers  were  known  only  by  number. 


428  BULLETIN  No.  127.  [August. 

TABLE  8.     PHYSICAL  SELECTION  OF  POTATOES  FOR  TABLE  QUALITY 


Variety. 

Selected  physically 
for  quality. 

No.  tubers 
used. 

No.  tubers 
yood  qual. 

No.  tubers 
med.  qual. 

No.  tubers 
poor  qual. 

K.  Six  Weeks  

good 

10 

8 

2 

0 

E.  Ohio  

poor 
good 

10 
10 

1 
10 

3 
0 

6 
0 

Houlton  Rose  

poor 
good 

10 
10 

2 
9 

3 
1 

5 
0 

Irish  Cobbler  

poor 
good 

10 
10 

0 
10 

2 
0 

8 
0 

Minister  

poor 
good 

10 

10 

3 

7 

2 
3 

5 
0 

Carman  No.  3  

poor 
good 

10 
20 

2 
16 

3 
3 

5 

1 

Rural  N.  Y.  No.  2... 
Green  Mountain  

poor 

good 
poor 

good 

20 

20 
20 

20 

4 

16 

5 

16 

5 

4 
5 

2 

11 

0 
10 

2 

State  of  Maine  

poor 
good 

20 
10 

3 
12 

7 
8 

10 
0 

Gem  of  Aroostock.  .  . 

poor 

good 
poor 

10 

10 
10 

2 

8 
0 

10 

10 
10 

8 

2 
10 

From  fifty  to  one  hundred  tubers  were  used  in  making  each  of 
these  selections,  all  of  which  were  grown  on  the  same  type  of  soil, 
(a  light  sandy  loam),  in  a  single  acre  plot.  In  making  selections  it 
was  very  noticeable  that  there  was  a  great  varietal  difference  in 
quality.  As  the  table  shows,  in  some  varieties  it  was  very  easy  to  se- 
lect tubers  of  good  cooking  quality,  while  in  other  varieties  no  sharp 
distinctions  could  be  made.  In  Rust  Proof,  Ionia  seedling,  Twen- 
tieth Century,  Gold  Coin  and  Early  Manistee  no  potato  of  good 
quality  could  be  found  although  there  were  a  number  classed  as 
medium.  This  is  perhaps  due  to  the  fact  that  this  was  the  first  year 
any  of  the  stock  had  been  grown  in  Connecticut  and  they  may  not 
have  been  adapted  to  the  particular  kind  of  soil  on  which  they  were 
rrrown.  I  have  learned  that  all  of  these  varieties  except  Rust  Proof 
sometimes  are  of  fair  quality  in  other  places. 

It  seems  evident  from  Table  8,  that  this  anatomical  difference 
is  a  varietal  character,  the  difference  between  varieties  being  very 
great.  The  difference  in  quality  within  the  variety,  however,  with 
as  similar  environmental  conditions  as  it  was  possible  to  give,  is 
almost  as  great  as  the  difference  between  varieties. 


IMPROVEMENT  OF  THE  POTATO. 


429 


Unfortunately  this  method  cannot  be  used  in  selecting  potatoes 
for  the  table,  on  account  of  the  necessity  of  their  cutting.  Whether 
the  extreme  variations  toward  homogeneous  structure  are  correl- 
ated with  quality  to  a  sufficient  degree  to  be  used  as  a  means  of  im- 
proving varieties  in  quality;  or  whether  fluctuations  due  to  slight 
environmental  differences  impossible  to  control,  obscure  the  herit- 
able variations,  is  now  being  investigated.  There  still  remains  the 
possible  explanation  that  the  other  factors  influencing  quality  are 
the  causes  of  the  great  varietal  differences,  although  our  work  in- 
dicates that  this  is  not  probable.  We  hope  that  it  will  be  possible 
to  use  the  method  in  determining  the  rejection  of  seedlings  after 
a  cross.  The  tubers  from  the  different  first  year  plants  should  be 
kept  in  different  bags  and  at  planting  time  selections  made  of  those 
tubers  having  a  large  cortical  layer  and  a  small  internal  medullary 
layer  branched  in  fine  divisions, — the  idea  being  to  have  the  in- 
ternal structure  of  the  potato  as  homogeneous  as  possible. 


FIG.  9.    CROSS  SECTIONS  OF  POTATO  OF  POOR  QUALITY.     SMALL  CORTICAL  LAYER  AND 

LARGE    THICK    INTERNAL    MEDULLARY    LAYER. 


OTHER  FACTORS  INFLUENCING  QUALITY 

i.  Color  of  skin. — Potatoes  from  seedlings  of  a  single  cross 
varying  in  color  of  skin  to  white,  light  brown,  pink  and  red  did  not 
show  any  greater  variation  in  quality  than  did  those  of  a  single 
color.  Hence  it  may  be  concluded  that  color  is  not  correlated  with 


430  BULLETIN  No.  127.  [August, 

quality.  We  found  varieties  of  all  colors .. except  the  purple  types 
which  were  ol  good  quality.  No  purple  skinned  potatoes  were 
available  which  were  of  a  size  that  indicated  maturity  and  this 
might  account  for  the  fact  that  they  were  of  a  poorer  quality. 

2.  Nature  of  skin. — Those  varieties  which  have  a  netted  skin 
were   found  to  be  generally  smooth-skinned  when  immature.     A 
corky  appearance   indicated   both  maturity   and   a  better  keeping 
quality.    In  some  cases  one  end  of  the  tuber  had  a  corky  netted  skin 
while  the  other  end  was  smooth;  these  were  generally  different  in 
internal  structure,  indicating  some  obstruction  to  perfect  develop- 
ment.   Very  rough-skinned  varieties  as  Russet  and  Scabproof  were 
in  general  less  susceptible  to  infection  with  potato  scab,  but  were 
neither  of  better  quality  nor  of  higher  starch  content  than  other 
varieties  grown  under  the  same  conditions ;   which  is  in  opposition 
to  the  conclusions  of  Krzymowski  (63). 

Lenticels  were  found  to  be  present  in  all  sizes  of  potatoes  and 
were  well  developed  in  individuals  of  most  varieties.  A  develop- 
ment of  strong  healthy  lenticels  indicates  maturity  in  the  tuber  al- 
though a  number  of  writers  have  pointed  out  that  possibly  scab  in- 
oculation takes  place  in  them. 

3.  Color  of  -flesh. — White  fleshed  tubers  are  the  only  ones  at 
present  accepted  in  the  American  markets  and  it  may  be  that  yel- 
low flesh  is  correlated  with   a  strong  flavor  and  a  poor   quality 
by  our  standard.     A  number  of  varieties  with  a  yellow  flesh  im- 
ported from  France  and  considered  by  the  French  to  be  of  prime 
quality   were   tested   and   were   gummy    and   hard    after   boiling. 
These  varieties  are  considered  of  good  quality  for  frying  and  for 
use  in  salads. 

4.  Shape. — Round  potatoes  as  Noroton     Beauty,    and     oblong 
round  potatoes  as  Early  Ohio  have  both  been  found  to  be  of  excel- 
lent table  quality,  but  the  general  popularity  and  prime  quality  of 
the  round  flat   (as  Irish  Cobbler)  and  short-oval-flat  types   (as  in 
Carman's  productions),  seem  to  support  Fischer's  view  that  po- 
tatoes of  these  types  are  better.     The  greater  possible  percentage 
of  cortical  layer  in  these  types  seems  to  be  sufficient  reason  for  the 
conclusion,  but  there  is  a  further  argument  in  the  fact  that  salad 
potatoes  are  usually  small  round  types,  or  long  slender  types  as  the 
Lady  Finger. 

5.  Depth  and  frequency  of  eyes. — Great  depth  of  eyes  will  be 
avoided  because  of  the  waste  in  peeling.     A  number  of  writers 
have  also  stated  that  extremely  deep  eyes  tend  toward  coarseness 
of  the  variety,  and  indeed  this  seems  to  be  the  case.     The  vital- 


1908.]  IMPROVEMENT  OF  THE  POTATO.  431 

ity  of  the  sprout  produced  varies  directly  as  the  size  and  depth 
of  the  eyes,  which  is  worthy  of  note  in  selection,  otherwise  types 
might  be  bred  with  eyes  too  shallow. 

The  number  of  eyes  has  a  marked  effect  on  the  quality,  due  to 
the  fact  that  the  internal  medullary  extends  a  branch  to  each  eye. 
This  makes  the  quality,  other  things  being  equal,  vary  inversely 
with  the  number  of  eyes.  This  variation  within  the  variety  is 
very  great,  varying  in  a  count  of  219  tubers  of  Rural  N'ew  Yorker 
No.  2  from  7  to  28. 

In  1902,  in  the  course  of  this  work,  189  tubers  of  the  variety 
Rural  New  Yorker  No.  2  had  been  analyzed  and  a  large  number 
having  been  cooked  were  found  to  be  of  very  good  quality  al- 
though the  average  dry  matter  content  was  only  20.74  percent. 
The  modes  for  eyes  in  this  lot  was  12. 

TABLE  9.    VARIATIONS  IN  NUMBER  OF  EYES  IN  RURAL  NEW  YORKER  No.  2,  1902 

No.  of  eyes  7  8  9  10  11  12  13  14  IS  16  17  18  19  20  21  22 
Frequencies  3  4  9  15  21  32  15  20  13  19  12  13  6  4  2  1 


In  1903,  219  tubers  of  the  Early  Ohio  variety  were  used,  and 
were  found  to  be  of  much  poorer  quality  than  those  used  in  1902, 
though  of  similar  size  and  of  pleasing  appearance.  The  average 
dry  matter  content  was  only  16.15  percent  or  4.59  percent  lower 
than  the  others.  The  mode  for  the  number  of  eyes  zvas  here  15 
as  compared  to  12  in  the  better  variety. 

TABLE  10.    VARIATIONS  IN  THE  NUMBER  OF  EYES  IN  EARLY  OHIO,  1903 

No.  of  eyes        7     8    9     10     11     12     13     14     15     16     17     18     19    20    21    22 
Frequencies       142      6     21     21     25     36     37     17     12     15       7     11       2       2 

6.  Type  of  soil. — It  is  well  known  that  the  physical  type  of 
soil  best  suited  for  the  growth  of  potatoes  is  a  light  sandy  loam. 
These  investigations  from  1902-1904  were  carried  on  in  the  black 
heavy  loam  characteristic  of  the  corn  belt  of  the  central  west  and 
in  1905-1906  on  a  light  sandy  loam  in  Connecticut.  No  stock 
from  the  same  strain  was  available  for  test,  and  as  the  influence 
due  to  climate  and  soil  is  unknown,  we  have  scarcely  a  warrant 
to  make  comparisons.  Published  analyses,  however,  show  a 
higher  percent  of  dry  matter  in  potatoes  grown  on  the  light  sandy 
loam?  and  the  quality  of  tested  tubers  from  the  same  variety 


432  BULLETIN  No.  127.  [August, 

though  not  from  the  same  stock,  was  perceptibly  better  on  this 
type  of  soil.  In  a  test  of  Early  Ohio  potatoes  on  the  heavy  loam 
soil,  planting*  to  a  depth  of  five  inches  gave  potatoes  of  a  much 
better  quality  than  potatoes  which  were  planted  to  a  depth  of 
three  inches.  The  same  was  true  of  Carman  No.  3  planted  on  a 
light  sandy  soil,  but  potatoes  planted  three  inches  deep  and  ridged 
at  the  last  cultivation  were  of  poorer  quality  than  those  unridged. 
This  coincides  with  Gilmore's  extensive  work  where  he  found  that 
about  five  inches  depth  showed  a  more  uniform  temperature  dur- 
ing the  season  than  did  other  depths. 

7.  Season  and  climate. — Season  and  climate  are  undoubtedly 
factors  in  determining  quality,  though  whether  they  have  an  in- 
fluence beyond  that  of  giving  the  plant  greater  or  less  chance  for 
producing  healthy,  mature  tubers,  it  is  impossible  to  say.     As  po- 
tatoes are  known  to  have  a  very  great  range  of  altitude  and  lati- 
tude when  conditions  of  soil  are  right,  we  are  inclined  to  think 
that  the  latter  is  the  only  influence. 

8.  Influence  of  fertilizers. — The  influence  of  fertilizers  seems 
to  be  primarily  if  not  solely  due  to  their  aid  in  producing  a  normal 
development  of  tubers.     That  is,  the  fertilizer  applied  must  correct 
abnormality  by  furnishing  an  element  of  fertility  which  is  lacking 
in  the  soil.     An  application  of  ordinary  quantities  of  an  essential 
element  which  is  already  present  in  the  soil  in  amounts  necessary 
to  a  normally   fertile  soil,  probably  has  no  marked  effect  either 
upon  the  crop  or  its  quality. 

Some  writers  have  maintained  that  the  use  of  potassium  sul- 
fate  gives  potatoes  of  better  quality  than  are  produced  with  the 
use  of  potassium  chlorid,  but  this  conclusion  is  opposed  by  other 
experiments.  There  is  probably  no  ill  effect  from  the  use  of  or- 
dinary amounts  (100  to  500  lb.*)  of  potassium  chlorid,  even  if 
excessive  use  of  chlorids  is  detrimental. 

The  following  table  shows  the  general  effect  of  fertilizers  upon 
quality.  In  an  experiment  planned  primarily  an  soil  fertility, 
sodium  nitrate  was  sown  at  the  rate  of  250  lb.  to  the  acre  over 
the  whole  plot  and  potassium  and  phosphorus  supplied  as  shown 
in  the  table.  The  numbers  here  shown  are  the  estimates  of  qual- 
ity of  all  of  the  tubers  produced  by  all  of  the  plants  of  one  row 
running  across  all  the  plots.  The  variety  used  was  Green  Moun- 
tain. The  land  was  very  poor  in  fertility  although  in  excellent 

*Potatoes  of  excellent  quality  have  been  tested,  which  were  grown  with  this  rate  of  potas 
sium  chlorid  but  no  comparisons  were  made  with  like  amounts  ot  potassium  sulfate. 


1908.] 


IMPROVEMENT  OF  THE  POTATO. 


433 


physical  condition  for  growing  potatoes.  It  was  known,  however, 
that  it  was  not  nearly  so  deficient  in  phosphorus  as  in  potassium. 
As  is  seen,  the  quality  grew  markedly  better  where  the  potassium 
chlorid  was  supplied  at  the  rate  of  300  Ib.  per  acre,  but  apparently 
very  little  difference  was  made  by  doubling  the  applications  of 
phosphorus. 

TABLE  n.    INFLUENCE  OF  FERTILIZERS  ON  QUALITY 


Plot 
No. 

Fertilizers 
applied 
per  acre. 

No. 
tubers 
pro- 
duced. 

No.  of  tubers  of  each  of  these  qualities. 

Good. 

Fair. 

Me- 
dium. 

Poor. 

Very 
poor. 

1 

Nothing-. 

81 

0 

5 

17 

25 

34 

Potassium 

chlorid 

2 

150  IDS., 

125 

1 

10 

33 

56 

25 

Bone  meal 

200  Ibs. 

Potassium 

chlorid 

3 

300  Ibs., 

121 

1 

12 

42 

40 

26 

Bone  meal 

100  Ibs. 

Potassium 

chlorid 

4 

300  Ibs., 

148 

3 

14 

56 

45 

30 

Bone  meal 

200  Ibs. 

Potassium 

chlorid 

5 

300  Ibs., 

135 

3 

19 

56 

37 

20 

Bone  meal 

400  Ibs. 

The  explanation  of  this  fact  is  apparent,  I  think,  in  the  next 
table,  which  shows  the  number  of  tubers  produced  of  different 
classes  of  30  grams  each.  There  was  simply  a  more  nearly  normal 
development  of  the  tubers  in  the  last  three  plots,  due  to  the  avail- 
ability of  more  potassium. 


434 


BULLETIN  No.  127. 


[August, 


CO 


CO 


00 


190$.' 


IMPROVEMENT  OF  THE  POTATO. 


435 


9.  Degree  of  maturity. — In  1902,  a  number  of  potatoes  of 
Rural  New  Yorker  No.  2  variety,  of  different  degrees  of  maturity, 
were  analyzed.  The  determinations  showed  that  the  greater  part 
of  the  total  nitrogen  is  developed  early  in  the  growth  of  the  tuber, 
while  the  starch  is  stored  up  later.  A  microscopical  examination 
showed  that  the  starch  grains  in  the  cells  of  the  immature  tubers 
are  small  in  size  and  few  in  number.  Starch  grains  in  the  cortical 
and  outer  medullary  layers  of  mature  tubers  averaged  about  75 
/*.  and  were  found  as  large  as  105  /*. ;  while  in  immature  tubers 
of  less  than  an  ounce  in  weight,  the  starch  grains  averaged  only 

25  f"  '       i  i , 

TABLE  13.     COMPOSITION  OF  TUBERS  OF  DIFFERENT  DEGREES  OF  MATURITY 
AVERAGES  OF  A  NUMBER  OF  TUBERS 


*Degree  of  maturity. 

Dry  matter, 
percent. 

Protein  fresh 
basis,  percent. 

Protein  dry 
basis,  percent. 

Very  immature. 

8  01 

1  22 

15  23 

Immature  .  . 

11  15 

1  66 

14  93 

Kairly  mature.  .  .  . 

16  70 

2  15 

12  85 

Mature  

21  20 

1  <H 

9  16 

These  tubers, — as  might  be  expected  from  their  composition, 
—increased  in  desirability  for  table  use  with  maturity  to  such  an 
extent  that  we  may  conclude  that  all  immature  potatoes  should  be 
rejected  for  cooking. 

This  fact  seems  a  reasonable  explanation  of  the  influence  that 
certain  other  minor  factors  seem  to  have  on  quality,  such  as  dis- 
tance apart  and  time  of  planting,  depth  and  frequency  of  cultiva- 
tion, etc.  In  fact  any  and  all  of  the  conditions  of  environment 
that  lead  to  the  normal  development  of  healthy,  mature  potatoes 
may  be  considered  as  contributing  toward  their  table  quality. 

As  a  result  of  these  tests,  we  are  led  to  the  following  conclu- 
sions regarding  quality : 

i.  Quality  depends  upon  the  following  factors:  a.  Homo- 
geneous anatomical  structure.  In  general,  quality  increases  with 
the  thickness  of  the  cortical  layer,  and  decreases  as  the  number 
of  eyes  increases.  A  variety  shape  which  gives  a  chance  for  a 
large  ratio  of  cortical  to  inner  medullary  layer,  is  an  advantage 
b.  Dry  matter  content.  This  must  be  such  that  the  cooked  starch 
fills  the  cells  to  their  bursting  point.  The  lower  limit  is  roughly 
estimated  at  18  percent,  c.  Maturity.  This  is  affected  by  all 

*Weig-hts  of  the  different  classes  were  approximately  50  jr.,  909  g-.,  150  g-.  and  250  g. 


436  BULLETIN  No.  127.  [August, 

factors  of  soil  physics,  soil  fertility,  cultivation  and  climate  dur- 
ing the  growing  period. 

2.  Under  like  conditions  of  environment,  variations   in  table 
quality  are  shown  as  varietal  characteristics  due  to  heritable  dif- 
ferences in  shape,  composition  and  physical  structure. 

3.  These  heritable  differences  can  probably  be  used  as  a  basis 
for  improvement  in  quality  when  originating  new  varieties. 

4.  There  are  also  variations  in  quality  within  a  variety  which 
are*  in  large  measure  due  to  immediate  external  conditions.     These 
fluctuations  obscure  the  heritable  variations  upon  which  improve- 
ment depends. 

5.  The  question  as  to  whether  partial  fluctuations  of  these  char- 
acters obey  the  same  laws  as  individual  fluctuations,  and  whether 
temporary  improvement  can  be  made  through  their  selection  is  yet 
undecided.     The  truth  of  Johannsen's  theory  of  the  fluctuations  of 
"pure  lines"  would  answer  this  in  the  negative. 


1908.] 


IMPROVEMENT  OF  THE  POTATO. 


437 


10.  VARIATION  OF  THE  POTATO  IN  CHEMICAL  COM- 
POSITION AS  A  BASIS  FOR  ITS  IMPROVEMENT 

In  1902  work  was  started  to  determine  whether  there  were 
sufficient  variations  of  the  proteid  content  within  a  variety  of 
potatoes  to  warrant  selection  of  individuals  high  in  protein  to 
endeavor  to  raise  the  average  protein  content  of  the  variety.  It 
was  expected  later  that  this  work  would  throw  some  light  upon  Jo- 
hannsen's  theory  that  in  "pure  lines"  (self- fertilized  lines),  fluc- 
tuations regress  completely  to  the  mode  of  the  pure  line  and  not 
toward  the  mode  of  the  general  population.  If  this  is  true,  abso- 
lutely no  change  could  be  made  by  selecting  partial  fluctuations. 
Johannsen's  work  was  not  reported  until  after  the  results  of  these 
two  seasons  had  been  obtained,  but  the  data  are  here  reported  just 
as  it  was  collected  in  1904. 

About  two  bushels  of  potatoes  of  uniform  type  were  selected 
from  a  carload  of  the  variety  Rural  New  Yorker  No.  2.  They 
were  all  grown  in  the  same  county  in  Wisconsin,  but  it  could  not 
be  definitely  stated  that  they  were  all  grown  in  the  same  field  or 
upon  the  same  type  of  soil  although  the  latter  is  likely.  They  were 
of  good  appearance  and  average  223  g.  in  weight.  The  smallest 
potato  used  weighed  141  g.  and  the  largest  328  g.  Over  one-half 
of  the  tubers  varied  less  than  30  g.  from  the  average.  The  table 
quality  was  good  for  the  time  of  the  year,  it  being  the  month  of 
May. 

Total  nitrogen,  dry  matter  and  specific  gravity  determinations 
were  made  on  one  hundred  seventy-nine  tubers.  The  total  nitrogen 
was  determined  by  the  regular  Kjeldahl  method;  dry  matter  by 
drying  to  constant  weight  at  IO4°C  in  a  glycerol  oven  in  a  current 
of  hydrogen ;  and  the  specific  gravity  by  the  weight  in  air  and  the 
weight  in  distilled  water  at  2O°C.  Considerable  variation  was 
shown  in  the  content  of  the  dry  matter  and  the  average  was  found 
to  be  very  low  for  potatoes  of  such  good  quality.  This  condensed 
table  shows  the  extent  of  the  variation,  the  extremes  being  15.18 
percent  and  28.27  percent. 

TABLE  14.     VARIATION  IN  DRY  MATTER  IN  RURAL  NEW  YORKER  No.  2,   CROP 

OF  1901 


Dry  matter,  percent  

15-16 

16-17 

17-18 

18-19 

19-20 

20-21 

21-22 

Frequency  

1 

7 

9 

17 

32 

39 

34 

Dry  matter   percent  .             ... 

22-23 

23-24 

24-25 

25-26 

26-27 

27-28 

28-29 

Frequency                  

18 

11 

3 

5 

2 

0 

1 

438 


BULLETIN  No.  127. 


[August, 


For  calculating  total  nitrogenous  matter  we  have  used  Frisby's 
and  Bryant's  (38)  factor  of  5.5  times  the  total  nitrogen.  The 
proteid  nitrogen  is  probably  about  55  percent  to  60  percent  of  these 
numbers,  but  as  it  is  still  questionable  as  to 'what  dietetic  value 
should  be  placed  upon  non-proteid  forms  of  nitrogen,  they  were 
not  determined.  The  total  nitrogenous  matters  are  reported,  cal- 
culated to  the  water  free  material.  The  extremes  are  6.63  percent 
and  15.69  percent. 

TABLE  15.     VARIATION  IN  TOTAL  NITROGENOUS  MATTER  IN  RURAL  NEW  YORKER 
No.  2,  CROP  OF  1901.    DRY  BASIS 


Nitrogenous 

matter  in 

percent  .  . 

6-7 

7-8 

8-9 

9-10 

10-11 

11-12 

12-13 

13-14 

14-15 

15-16 

Frequency. 

3 

4 

7 

18 

33 

43 

30 

23 

12 

6 

This  table  shows  a  surprising  variability  in  composition  in 
potatoes  of  the  same  variety.  The  extremely  high  percentage  of 
nitrogenous  constituents  shows  that  there  may  be  a  basis  for  the 
origination  of  a  variety  equal  in  proteid  content  to  a  number  of 
the  varieties  of  dent  maize  now  grown,  could  a  variety  with  the 
composition  of  the  highest  fluctuations  be  perpetuated.  Certainly, 
in  this  variety  at  least,  the  tubers  do  not  deserve  to  be  ranked  as 
solely  a  starch  food. 

A  number  of  points  were  observed  in  looking  over  the  complete 
data  which  are  too  bulky  to  publish. 

1.  The  nitrogen  content  does  not  vary  directly  with  the  num- 
ber of  eyes.     Therefore,  in  potatoes  of  the  same  size,  many  stems 
have  no  greater  amount  of  nitrogen  to  draw  upon  in  sprouting, 
than  have  a  few. 

2.  Variations  in  nitrogen  content  are  not  correlated  with  par- 
ticular shapes. 

3.  Smaller,   younger   tubers   are   richer   in   nitrogen;    that   is, 
there  is  stored  early  in  the  formation  of  the  tuber  a  relatively  larger 
proportion  of  the  total  nitrogen  than  of  starch. 

4.  The  error  in  determining  starch  from  specific  gravity  tables 
is  much  greater  than  is  generally  supposed.     For  example,  tuber 
No.  82  contains  14.32  percent  nitrogenous  matter,  specific  gravity 
1.090;   while  tuber  No.  69  contains  7.39  percent  nitrogenous  mat- 
ter, specific  gravity  1.091. 


JQ08. 


IMPROVEMENT  OF  THE  POTATO. 


439 


SELECTIONS  FOR  PLANTING,  1902 

To  endeavor  to  determine  whether  these  fluctuations  in  a  chem- 
ical constituent  are  transmitted  by  tuber  propagation,  two  plots 
were  planted,  one  of  high  nitrogen  selections  and  one  of  low  nitro- 
gen. This  gives  a  check  upon  the  seasonal  and  soil  variations.  The 
selections  were  made  upon  the  fresh  substance,  because  this  is  their 
market  condition,  and  because  the  dry  matter  determinations  were 
not  finished  soon  enough  to  make  selections  on  the  water  free  basis 
practicable. 

As  may  be  seen  in  the  table,  potatoes  were  chosen  with  as 
nearly  as  possible  the  same  average  weight.  The  low  protein  se- 
lections, however,  averaged  about  i8g.  heavier  per  tuber. 

The  average  nitrogenous  matter  in  the  high  portein  plot  was 
2.95  percent  of  the  fresh  substance  and  14.07 'percent  calculated  to 
the  water  free  substance.  The  following  data  were  taken  on  each 
tuber.  The  long,  medium  and  short  diameters  give  a  fair  indica- 
tion of  the  shapes  of  the  tubers  : 

TABLE  16.    HIGH  PROTEIN  SELECTIONS  IN  1902 


No. 

Wt. 
per 

cent. 

Long 
diam. 

Me- 
dium 
diam. 

Short 
diam. 

No 

eyes 

Specific 
gravity. 

Dry 
matter 
percent. 

Nitroge- 
nous 
matter, 
fr.  b. 
percent. 

Nitrog-e- 
nous 
matter, 
dry  b., 
percent. 

44 

246 

98 

75 

55 

10 

1.095 

22.09 

2.93 

13.28 

63 

279 

115 

68 

60 

14 

1.082 

19.49 

3.05 

15.69 

68 

178 

90 

65 

53 

11 

1.090 

21.02 

2.95 

14.03 

80 

198 

88 

70 

55 

9 

1.097 

20.74 

2.99 

14.44 

82 

232 

100 

68 

52 

12 

1.090 

20.62 

2.95 

13.29 

99 

182 

95 

60 

55 

16 

1.088 

22.21 

2.95 

13.29 

104 

294 

122 

70 

58 

17 

1.091 

21.21 

2.87 

13.54 

107 

228 

115 

62 

52 

18 

1.096 

21.41 

2.90 

13.53 

111 

155 

75 

62 

55 

7 

1.095 

22.41 

•    2.90 

12.94 

113 

221 

98 

65 

58 

19 

1.088 

19.19 

2.91 

15.16 

117 

141 

90 

57 

46 

13 

1.100 

23.31 

3.09 

13.25 

129 

199 

91 

66 

54 

12 

1.087 

19.75 

2.84 

14.41 

137 

177 

85 

63 

48 

10 

1.096 

20.98 

2.90 

13.79 

147 

166 

90 

64 

50 

10 

1.088 

20  45 

3.12 

15.30 

166 

190 

90 

65 

51 

11 

1.098 

20.84 

2.95 

14.13 

Aver  . 

205.7 

12.6 

1.092 

21.05 

2.95 

14.07 

Each  potato  was  quartered  and  each  quarter  planted  in  a  hill. 
The  hills  were  four  by  two  feet  apart.  The  planting  could  not  be 
done  on  account  of  press  of  other  work  until  June  tenth. 

In  exactly  the  same  manner,  end  to  end  with  these  selections, 
were  planted  the  following  low  protein  selections,  which  averaged 
1.78  percent  nitrogenous  matter  in  the  fresh  substance,  and  8.75 
percent  calculated  to  water  free  basis. 


440 


BULLETIN  No.  127. 


[August, 


FIG.  10.    POTATO  FRUIT.     NATURAL  SIZE. 

The  plants  in  the  two  plots  were  up  about  the  same  time,  but 
owing  to  the  wet  season  and  late  planting  on  undrained  land,  were 
not  vigorous.  They  were  cultivated  three  times  and  sprayed  twice 
with  Paris  green.  Tip  burn  and  Paris  green  injury  combined  to 
kill  the  plants  very  early.  All  plants  on  the  two  plots  died  at  prac- 
tically the  same  time. 

Each  potato  planted  produced  from  six  to  twenty  tubers,  but 
these  were  quite  small,  few  being  of  marketable  size.  The  tubers 
from  the  low  protein  plot  were  somewhat  larger  than  those  from 
the  high  protein  plot. 


1908.] 


IMPROVEMENT  OF  THE  POTATO. 


441 


Composite  samples  from  the  progeny  of  each  tuber  were  made, 
and  total  nitrogen  and  moisture  determined,  as  shown  in  the  fol- 
lowing tables : 

TABLE  17.     Low  PROTEIN  SELECTIONS  IN  1902 


No. 

Wt.gr. 

L,ong 
diam. 

Me- 
dium 
diam. 

Short 
diam. 

No. 
Eyes. 

Specific 
Gravity. 

Dry 
Matter, 
percent. 

Protein 
fr.  b. 
percent. 

Protein 
dry  b. 
percent. 

3 

168 

86 

61 

49 

14 

1.099 

22.48 

1.91 

8.50 

6 

234 

113 

65 

52 

19 

1.092 

20.04 

1.93 

9.64 

23 

256 

107 

68 

53 

16 

1.087 

18.13 

1.64 

9.03 

51 

248 

104 

61 

57 

22 

1.091 

20.17 

1.79 

8.86 

59 

244 

101 

71 

52 

11 

1.098 

24.37 

1.65 

6.77 

65 

220 

105 

70 

55 

20 

1.102 

26.06 

1.72 

6  63 

69 

229 

105 

65 

55 

15 

1.091 

23.50 

1.73 

7.39 

85 

199 

105 

74 

53 

12 

1.081 

16.35 

1.81 

11.11 

102 

243 

100 

71 

56 

13 

1.084 

17.54 

1.87 

10,66 

123 

221 

99 

66 

53 

15 

1.096 

21.45 

1.56 

7.28 

140 

198 

110 

63 

46 

17 

1.103 

23.15 

1.64 

7.08 

158 

229 

104 

70 

56 

17 

1.089 

19.10 

1.70 

8.91 

168 

170 

91 

62 

47 

10 

1.089 

19.86 

1.93 

9.72 

173 

272 

99 

73 

60 

14 

1.083 

19.73 

1.94 

9.83 

179 

218 

95 

67 

58 

10 

1.089 

19.65 

1.93 

9.81 

Aver. 

223 

14.9 

1.092 

22.10 

1.78 

8.75 

TABLE  18.    HIGH  PROTEIN  PLOT  (CROP  OF  1902) 
(Weights,  extremes  5  g.  and  150  g.,  average  38  g.) 


Row 

From 

Dry  matter 

Nitrogenous 

Nitrogenous 

No. 

potato  No. 

percent. 

matter,  fr.  b. 

matter,  dry  b. 

1 

44 

13.55 

2.48 

18.48 

2 

63 

13.56 

2.51 

18.46 

3 

68 

10.50 

1.24 

11.83 

4 

80 

11.50 

1.39 

12.11 

*5 

82 

5.43 

1.04 

19.04 

*6 

99 

6.33 

1.18 

18.59 

7 

104 

14.54 

2.17 

14.96 

8 

107 

10.75 

1.28 

11.96 

9 

111 

8.00 

1.58 

19.81 

*10 

113 

7.25 

1.65 

22.81 

*11 

117 

7.00 

1.66 

23.74 

12 
13 

129 
137 

14.57 
13.92 

1.79 
2.00 

12.29 
14.35 

14 

147 

13.00 

2.25 

17.33 

15 

166 

14.83 

2.26 

15.26 

General  average 

10.98 

1.765 

16.73 

Average  after  rejection 

13.07 

1.937 

14.70 

*Very  small,  rejected. 


442 


BULLETIN  No.  127. 


[August, 


TABLE  19.     Low  PROTEIN  PLOT   (CROP  OF  1902) 
(Weights,  extremes  10  g.  and    180  g.,  average  68  g.) 


Row 

From 

Dry  matter 

Nitrogenous 

Nitrogenous 

No. 

potato  No. 

percent. 

matter,  fr.  b. 

matter,  dry  b. 

1 

3 

21.20 

1.94 

9.16 

2 

6 

16.42 

2.32 

14.16 

3 

23 

16.33 

2.10 

12.86 

*4 

51 

7.50 

1.25 

16.68 

5 

59 

11.15 

1.66 

14.93 

*6 

65 

8.26 

1.24 

15.02 

7 

69 

15.42 

2.31 

14.96 

*8 

85 

8.28 

1.16 

14.00 

9 

102 

15.33 

2.18 

14.27 

10 

123 

16.02 

1.92 

12.00 

11 

140 

14.55 

1.49 

10.20 

12 

158 

14.50 

2.02 

13.95 

*13 

168 

12.50 

1.12 

8.94 

14 

173 

17.23 

2.23 

12.95 

IS 

179 

16.16 

2.06 

12.75 

General  average 

14.056 

1.80 

13.12 

Average  after  rejection 

15.56 

1.945 

12.59 

*Very  small,  rejected. 

The  general  averages  here,  after  rejecting  the  results  from  such 
hills  as  were  far  below  marketable  size  indicate  that  there  is  no 
definite  response  to  selection  for  high  or  low  prcrtein.  It  is  true 
that  the  average  of  nitrogenous  matter  when  calculated  to  the 
water  free  basis  is  2.11  percent  higher  in  the  crop  from  the  high 
nitrogen  selections  than  in  the  crop  from  the  low  nitrogen  selec- 
tions. This,  however,  is  wholly  due  to  the  difference  in  the  aver- 
age contents  of  dry  matter,  for  the  nitrogenous  matter  when  cal- 
culated to  the  fresh  substance,  are  practically  the  same. 

There  is  an  indication  that  the  low  protein  potatoes  are  quicker 
to  mature,  for  in  the  same  growing  period  they  had  elaborated 
about  twice  as  much  fresh  material,  which  contained  2.5  percent 
more  dry  matter  than  the  high  protein  potatoes. 

The  poor  development  of  the  potatoes  this  season  necessitated 
a  return  to  other  seed  for  the  continuation  of  the  experiment.  This 
reduces  the  value  the  results  of  the  second  might  have,  as  it  was 
the  intention  to  continue  selecting  from  the  same  stock,  with  the 
hope  of  testing  a  possible  cumulative  effect  of  selection. 


1908.] 


IMPROVEMENT  OF  THE  POTATO. 


443 


SELECTIONS  FOR  PLANTING,  1903 

The  experiment  was  continued  in  1903,  with  the  variety  Early 
Ohio,  which  was  considered  to  give  better  yields  on  Illinois  soil. 
Unfortunately,  the  seed  tubers  which  were  obtained  had  been  grown 
in  southern  Illinois  on  soil  of  an  entirely  different  type  from  that 
upon  which  they  were  to  be  planted  in  the  experiment,  and  there  is 
no  means  of  knowing  whether  the  stock  was  adapted  to  the  latter 
type. 

These  potatoes  were  of  different  type  from  those  used  in  1902. 
the  Early  Ohio  being  oblong-cylindrical.  The  average  weight  was 
smaller  and  the  cooking  quality  poorer  than  those  of  the  previous 
year.  They  were  slightly  infected  with  scab,  but  were  fairly  typ- 
ical of  the  variety. 

Two  hundred  nineteen  individual  tubers  were  analyzed  in  the 
same  manner  as  those  of  the  year  before,  with  the  result  that  fully 
as  great  variation  in  individuals  was  found  in  this  variety. 

Comparing  the  two  varieties  used  (1902  and  1903),  which  of 
course  is  not  strictly  fair,  owing  to  their  being  the  product  of  dif- 
ferent soils  and  seasons,  it  is  seen  that  the  higher  average  dry  mat- 
ter is  shown  in  the  round-flat  variety,  which  is  in  accord  with 
Fischer's  theory. 

The  dry  matter  fluctuations  were  from  10.55  percent  to  30.96 
percent,  with  an  average  of  16.15  percent  and  a  mode  between 
16.0  percent  and  17.0  percent. 

TABLE  20.    VARIATIONS  IN  DRY  MATTER.     (CROP  OF  1902,  EARLY  OHIO) 


Dry  matter,  per- 
cent 

10-11 
4 

11-12 

5 

12-13 

7 

13-14 
20 

14-15 
19 

15-16 
44 

16-17 
54 

17-18 

27 

18-19 

24 

19-20 
13 

20-21 
3 

Frequencies.  .  .  . 

The  average  nitrogenous  matters,  calculated  to  fresh  basis  is 
2.43  percent,  and  calculated  to  water  free  basis  is  15.21  percent. 
The  variations  in  total  nitrogenous  matter  are  shown  in  the  fol- 
lowing table : 


444 


BULLETIN  No.  127. 


[August, 


TABLE  21.    VARIATIONS  IN  TOTAL  NITROGENOUS   MATTER.     (CROP   OF  1902,  EARLY 

OHIO.    DRY  BASIS) 


Nitrogenous 
matter,  percent 

7-8 

8-9 

9-10 

10-11 

11-12 

12-13 

13-14 

14-15 

15-16 

16-17 

17-18 

Frequencies  

1 

1 

0 

1 

7 

14 

39 

40 

46 

27 

11 

Nitrogenous 
matter,  percent 

18-19 

19-20 

20-21 

21-22 

22-23 

23-24 

24-25 

25-26 

26-27 

27-28 

Frequencies.  .  .  . 

12 

8 

2 

0 

0 

0 

0 

1 

0 

1 

The  mode  of  nitrogenous  matter  is  here  between  15  percent 
and  1 6  percent.  This  is  an  amount  of  nitrogenous  matter  not  to 
be  despised.  If  the  nitrogenous  matter  could  be  raised  in  the  same 
proportion,  when  by  cultivation  under  better  conditions,  a  higher 
dry  matter  is  obtained,  there  would  be  a  food  containing  at  least 
as  much  actual  proteid  nitrogen  as  many  varieties  of  maize.  It  is 
highly  probable  that  the  two  extreme  high  variations  should  be  dis- 
regarded as  errors,  although  potato  No.  13  with  a  content  of  nitrog- 
enous matter  of  27.46  percent,  weighed  only  87  grams,  which 
might  account  for  rather  high  nitrogen  content.  The  other  tubers 
varied  in  weight  from  150  to  300  grams. 

Twenty  tubers  were  selected  for  the  high  protein  plot  and  fif- 
teen for  the  low  protein  plot,  selecting  on  the  fresh  basis,  as  before. 
The  analyses  of  the  individuals  selected  for  planting  are  shown  in 
Tables  22  and  23. 

TABLE  22.    HIGH  PROTEIN  SELECTIONS.     1903 


Planted  in 
row  No. 

Wt.  Nit.  matter 
fresh  basis. 

Dry  matter, 
percent. 

Nit.  matter, 
dry  basis. 

Sp.  gr. 

1 

2.78 

14.28 

19.42 

1.063 

2 

3.12 

15.53 

20.01 

1.058 

3 

,  2.93 

10.66 

27.46 

1.092 

4 

3.03 

15.10 

20.04 

1.060 

5 

2.78 

14.93 

18.60 

1.059 

6 

2.78 

15.35 

18.10 

1.061 

7 

2.80 

10.74 

25.91 

1.062 

8 

2.92 

16.74 

17.42 

1.059 

9 

2.90 

18.85 

15.36 

1.064 

10 

2.80 

15.66 

17.85 

1.056 

11 

2.79 

17.60 

15.81 

1.062 

12 

2.77 

15.34 

18.06 

1.062 

13 

2.83 

18.96 

14.91 

1.069 

14 

2.81 

16.99 

16.53 

1.069 

15 

2.86 

17.99 

16.39 

1.067 

16 

2.93 

19.62 

14.93 

1.074 

17 

2.83 

17.36 

16.31 

1.063 

18 

2.85 

18.94 

15.04 

1.066 

19 

2.77 

16.18 

17.10 

1.066 

20 

2.77 

17.49 

15.85 

1.060 

General  av. 

2.85 

16.215 

18.055 

1.064 

1908.] 


IMPROVEMENT  OF  THE  POTATO. 
TABLE  23.    Low  PROTEIN  SELECTIONS.     1903 


445 


Planted  in 

Wt.  Nit.  matter 

Dry  matter 

Nit.  matter 

row.  No. 

fresh  basis. 

percent. 

dry  basis. 

Sp.  gr. 

1 

1.97 

13.37 

14.71 

1.054 

2 

2.01 

11.30 

17.74 

1.037 

3 

1.88 

13.08 

14.40 

1.038 

4 

2.02 

14.03 

14.32 

1.026 

5 

1.46 

10.77 

13.56 

1.040 

6 

1.68 

11.17 

15.01 

1.034 

7 

1.96 

12.62 

15.55 

1.044 

8 

1.72 

12.22 

14.09 

1.045 

9 

1.80 

11.86 

15.16 

1.045 

10 

1.97 

13.26 

14.81 

1.050 

11 

1.60 

12.93 

12.39 

1.045 

12 

1.38 

19.30 

7.14 

1.034 

13 

1.98 

16.81 

11.78 

1.059 

14 

1.68 

19.99 

8.39 

1.032 

15 

1.65 

14.30 

11.53 

1.043 

General  av. 

1.78 

13.80 

13.37 

1.0417 

There  was  a  noticeable  difference  this  year  in  the  contents  of 
dry  matter  of  the  two  selections.  The  tubers  planted  in  the  high 
protein  plot  average  2.42  percent  higher  than  those  planted  in  the 
low  protein  plot.  This  reduces  the  average  difference  in  content  of 
nitrogenous  matter  between  the  tubers  of  the  two  classes,  but 
there  is  still  a  difference  of  4.69  percent,  when  calculated  to  the 
water  free  basis.  This  matter  is  of  interest  because  it  definitely 
shows  that  in  mature  tubers,  a  high  percentage  of  nitrogenous  mat- 
ter is  not  correlated  with  a  low  dry  matter  content.  This  is  addi- 
tional evidence  that  potatoes  of  good  quality,  other  things  being 
equal,  may  be  high  in  nitrogen.  The  average  weight  of  the  selec- 
tions for  the  low  protein  plot  was  nine  grams  higher  than  those  for 
the  high  protein  plot. 

The  tubers  were  quartered  and  were  planted  in  the  same  man- 
ner as  in  the  year  before,  but  on  slightly  better  soil.  The  planting 
was  done  May  18,  1903,  and  the  potatoes  were  up  June,  second. 
Every  cutting  grew,  but  the  growth  was  not  luxuriant.  It  is 
thought  that  the  seed  may  have  been  injured  by  the  formalin  treat- 
ment for  scab.  The  plots  were  given  ordinary  farm  cultivation, 
and  were  sprayed  three  times  with  Paris  green  and  once  with  Bor- 
deaux mixture. 

The  plants  in  both  plots  succumbed  to  tip  burn  and  Paris  green 
injury  about  the  same  time.  The  crop  was  larger  than  that  of  the 
year  before,  but  not  nearly  all  of  the  tubers  were  of  marketable 
size.  The  potatoes  were  of  different  degrees  of  immaturity,  but  were 
sufficiently  mature  to  make  a  fair  comparison.  Seventy-five  per- 
cent by  weight  of  the  crop  from  the  high  protein  plot  averaged  75 


446 


BULLETIN   NO.    127. 


[August  t 


grams  in  weight,  while  seventy-five  percent  by  weight  of  the  crop 
from  the  low  protein  plot  averaged  70  grams  in  weight.  The 
analyses  of  composite  samples  are  given  in  the  following  tables : 

TABLE  24.    HIGH  PROTEIN  PLOT.     (CROP  OF  1903) 


Row  No. 

Dry  matter, 
percent. 

Nit.  matter, 
fresh  basis. 

Nit.  matter, 
dry  basis. 

1 

17.01 

1.88 

11.08 

2 

18.04 

1.72 

9.57 

3 

19.32 

1.98 

10.24 

4 

17.65 

2.04 

11.57 

5 

15.50 

1.88 

12.13 

6 

17.58 

2.00 

11.35 

7 

17.19 

1.90 

11.04 

8 

17.75 

2.32 

13.08 

9 

13.48 

1.97 

14.63 

10 

13.68 

1.62 

11.84 

11 

15.44 

1.50 

9.75 

12 

16.23 

1.62 

9.98 

13 

14.53 

1.44 

9.95 

14 

16.11 

1.87 

11.62 

15 

15.02 

1.75 

11.67 

16 

15.84 

1.71 

10.78 

17 

14.02 

1.51 

10.82 

18 

15.98 

1.39 

8.71 

19 

14.31 

1.28 

8.96 

20 

13.83 

1.27 

9.16 

Gen.  ave.  .  . 

15.93 

1.73 

10.90 

TABLE  25.    Low  PROTEIN  PLOT.     (CROP  OF  1903.) 


Row  No. 

Dry  matter, 
percent. 

Nit.  matter, 
fresh  basis. 

Nit.  matter, 
dry  basis. 

1 

14.80 

1.23 

8.32 

2 

14.11 

1.20 

8.47 

3 

15.93 

1.44 

9.06 

4 

15.72 

1.30 

8.31 

5 

15.61 

1.36 

8.76 

6 

14.68 

1.58 

10.76 

7 

13.87 

1.28 

9.27 

8 

16.41 

1.36 

8.26 

9 

15.94 

.46 

9.15 

10 

14.92 

.37 

9.23 

11 

14.98 

.30 

8.69 

12 

14.38 

.76 

12.28 

13 

13.91 

.31 

9.42 

14 

15.28 

.52 

9.96 

15 

16.21 

15.1 

9.32 

Gen.  ave.  .  . 

15.12 

1.40 

9.29 

IMPROVEMENT  OF  THE  POTATO.  447 

No  very  definite  conclusions  can  be  drawn  from  this  one  sea- 
son's work,  yet  in  comparing  a  possible  inheritance  of  variations, 
the  difference  of  .81  percent  in  dry  matter  is  noteworthy.  It  should 
be  remembered  that  the  low  protein  potatoes  were  larger  and  from 
them  should  have  ordinarily  been  expected  the  higher  dry  matter. 
The  difference  in  total  nitrogenous  matter,  in  favor  of  the  high 
protein  plot  was  0.33  percent  upon  the  fresh  sample  and  1.61  per- 
cent upon  the  dried  sample.  The  regression  of  each  plot  toward 
the  same  type  in  percentages  of  dry  matter  and  nitrogenous  mate- 
rial is  great  but  no  more  than  would  have  been  expected  from  seed 
propagated  selections. 

Note. — This  experiment  is  being  continued  on  a  somewhat  dif- 
ferent plan.  A  variety  of  potatoes  has  been  produced,  coming  from 
a  single  tuber  of  a  seedling  of  four  years  ago.  With  these  tubers 
two  plots  are  being  carried  on,  one  for  high  and  one  for  low  nitro- 
gen. It  is  expected  by  thus. having  a  check  upon  the  effects  of  soil,, 
and  having  to  deal  with  an  accurately  estimated  character,  to  be 
able  definitely  to  demonstrate  whether  there  is  inheritance  of  asex- 
ual fluctuations. 

GENERAL  STATEMENTS 

The  improvement  of  our  present  varieties  of  potatoes  in  yield- 
ing power,  and  the  enhancing  of  particularly  valuable  characters 
through  breeding  and  selection  have  been  shown  in  the  foregoing 
pages  to  be  broad  and  many  sided  questions.  They  are  beset  with 
difficulties  such  as  are  attendant  on  the  improvement  of  no  other 
important  field  crop.  But  if  the  questions  are  difficult,  some  Gf  them 
are  far  reaching  in  their  bearing  and  the  subject  seems  alike  wor- 
thy ^the  attention  of  the  biologist  seeking  experimental  evidence 
concerning  the  meaning  of  sex  and  the  inheritance  of  fluctuating 
characters;  and  the  practical  breeder  whose  relative  success  in  the 
production  of  new  varieties  is  measured  by  dollars  and  cents. 

The  use  of  other  tuber  bearing  species  of  Solanum  as  a  starting 
point  for  new  varieties  has  not  yet  produced  anything  of  value. 
Hope  is  still  entertained  that  5\  Commersonii  crossed,  or  hybrid- 
ized, with  S.  tuberosum  will  finally  produce  something  that  is  dis- 
ease resistant  and  satisfactory  in  other  respects.  The  present  evi- 
dence, however,  seems  to  point  towards  some  correlation  of  quality 
with  susceptibility  to  disease,  so  that  definite  knowledge  of  the 
physiological  meaning  of  fungus  resistance  is  most  probably  the 
key  to  the  door  we  must  enter. 


448  BULLETIN  No.  127.  [August, 

The  fairly  extensive  recorded  history  of  5\  tuberosum  for  three 
hundred  years  is  interesting  to  the  student  of  changes  under  do- 
mestication, in  that  the  changes  which  have  taken  place  in  the  plant 
;have  been  almost  entirely  in  the  selected  part,  the  tuber.  Even  the 
•change  in  the  tubers  seems  to  be  largely  a  matter  of  lesser  numbers 
.and  larger  size  per  plant.  The  minor  distinctions  that  have  sepa- 
rated modern  varieties  have  been  in  the  main  those  of  shape  and 
color.  Slight  differences,  provided  the  variety  is  a  fairly  high 
yielder,  have  been  the  cause  of  a  large  number  of  names,  but  in  the 
United  States,  at  least,  the  productions  of  scientific  breeders  com- 
paratively few  in  number,  furnish  practically  the  entire  crop  of  the 
country. 

Methods  of  hybridizing  the  potato  are  comparatively  simple, 
but  the  variation  of  the  varieties  in  their  ability  to  furnish  viable 
pollen  has  been  a  source  of  disappointment  with  a  great  many 
varieties  possessing  other  particularly  good  characters.  A  problem 
here  is  to  find  means  of  stimulating  the  production  of  pollen  in 
these  varieties.  This  matter  is  also  of  special  theoretical  interest 
in  its  bearing  on  the  production  of  sex. 

The  method  of  propagating  the  potato  has  seriously  increased 
the  number  of  errors  .in  making  comparative  field  tests  during  the 
establishment  of  varieties.  The  fact  that  the  seedlings  must  be 
grown  several  years  in  the  comparison  test  before  making  definite 
selections,  makes  care  in  this  respect  still  more  important.  The  dis- 
covery of  characters  in  the  young  plant  which  are  correlated  with 
characters  in  the  tuber  would  be  of  great  advantage  in  shortening 
the  time  of  their  comparison  before  final  rejection  of  the  unfit. 
Some  work  has  already  been  done  in  this  direction. 

Possible  methods  of  improvement  are  three : 

1.  The  crossing  of  desirable  plants  and  raising  of  many  seed- 
lings under  controlled  conditions. 

2.  Selections  of  the  most  desirable  fluctuations  among  the  plants 
and  tubers  of  a  variety. 

3.  Selection  of  discontinuous  variations^  and  a  study  of  ways 
of  causing  them,  a  possible  example  being  the  so-called  graft-hybrid. 

That  advance  is  possible  by  the  first  method  is  admitted  from 
the  results  of  its  use  by  the  best  breeders.  More  data  as  to  the  best 
details  for  work  in  use  of  this  method,  however,  are  very  desirable. 
Whether  results  can  be  obtained  by  the  second  method  has  not  been 
definitely  proved.  The  data  here  shown  which  do  point  to  the  af- 
firmative, are  not  conclusive.  Isolated  cases  of  improvement  might 
reasonably  be  explained  as  due  to  mutations. 


I9o8.]  IMPROVEMENT  OF  THE  POTATO.  449 

The  hypothesis  of  degeneration  seems  to  have  little  ground 
either  in  theory  or  in  practice.  Disease  control  is  here  of  para- 
mount importance. 

Table  quality,  according  to  the  American  standard,  depends  pri- 
marily upon  homogenous  structure  of  the  tuber,  when  mature  tu- 
bers of  a  fair  percentage  dry  matter  are  compared.  This  condition 
is  to  a  large  extent  a  varietal  character  and  as  such  is  probably 
capable  of  improvement.  That  this  can  be  done  by  selection  of 
tubers  within  a  variety  has  not  yet  been  definitely  determined,  but 
is  improbable. 

Tubers  with  a  total  content  of  nitrogenous  matter  beyond  the 
average  for  maize  (calculated  to  dry  basis)  have  been  found.  It 
has  been  shown  that  a  high  nitrogen  content,  at  least  within  the 
limit  found,  is  not  through  any  law  of  composition,  opposed  to  our 
conception  of  quality. 

That  varieties  can  be  produced  with  a  much  higher  food  value 
because  of  their  higher  nitrogen  content,  by  selection  of  seedlings 
from  their  chemical  analysis  is  not  to  be  doubted. 


450  BULLETIN  No.  127.  [August, 


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